Fix for xml_easy_content() for nodes with no content

Support for self-closing tags

Instead of crushing xml_easy_content() returns now NULL when there's no content.

Fixed xml.c verbosity in debug builds. See [Issue 1](https://github.com/ooxi/xml.c/issues/1)

Squashed commit of the following:

commit 9ed7fee198
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 18:20:04 2012 +0100

    xml.c parser verbosity

commit 97d4cbade8
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 18:19:21 2012 +0100

    xml.c parser verbosity

commit 8c5493710b
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 18:17:13 2012 +0100

    xml.c parser verbosity

commit 3a793c8c7d
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 18:16:37 2012 +0100

    xml parser verbosity

Added xml_open_document API call to read a XML document from file

Squashed commit of the following:

commit 3501a6d4a4
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:10:37 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:10:04 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:09:56 2012 +0100

    Open XML document...

commit be3baa3d99
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:09:48 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:07:35 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:06:58 2012 +0100

    Open XML document...

commit 4af3334803
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:05:24 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:04:30 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:02:53 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:02:03 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:01:14 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 16:00:25 2012 +0100

    Open XML document...

commit f7c905130d
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 15:59:31 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 15:57:29 2012 +0100

    Open XML document...

commit 1b3fa5f684
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 15:45:03 2012 +0100

    Open XML document...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 15:41:48 2012 +0100

    Open XML document...

commit 64418dcb81
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 15:41:06 2012 +0100

    Open XML document...

commit 54061a0e3b
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 15:40:39 2012 +0100

    Open XML document...

commit e776734fa2
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 15:39:39 2012 +0100

    Open XML document...

commit 81bbf1e0c3
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 15:38:36 2012 +0100

    Open XML document...

New easy xml interface

Squashed commit of the following:

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 14:51:19 2012 +0100

    Easy development...

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    Easy development...

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    Easy development...

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    Easy development...

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    Easy development...

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    Easy development...

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    Easy development...

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    Easy development...

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    Easy development...

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    Easy development...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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    Easy interface...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
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    Easy interface...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
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    Easy interface...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
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    Easy interface...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
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    Easy interface...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 14:04:36 2012 +0100

    Easy interface...

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Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 13:59:29 2012 +0100

    Easy interface...

commit 9bb88f95d4
Author: ooxi <85fcd0ef4ec8@f977375cdcd6.anonbox.net>
Date:   Thu Nov 1 13:59:01 2012 +0100

    Easy interface...

Similar to the GLib Markup parser, which also just parses an xml subset, xml.c is a simple, small and self contained xml parser in one file. Ideal for embedding into other projects without the need for big external dependencies.