Update documentation.

Provide default states for input and output.

Allow MIDI input to be filtered through MIDI channels.

Restrict Yes/No actions in same 2-octave span.

The file has been updated upon introducing MIDI controller input
support.

Make device handling opt-in.

Ensure that initial loading of the config saves the values back to the
config file, in order to account for fallback values.

We use minIni to parse ini files instead of implementing our own. This
is useful for config modifiable by the user, such as controls.

However, we haven't implemented a fault-tolerant config that writes to
the config when the existing file is corrupted or non-existent. We will
have to define a "save" as soon as we have all values defined for our
in-memory config, regardless if we have retrieved the values
successfully or provided default hardcoded values.

Since we use an external dependency to manage our configs, the CMake
config must be modified and the source files included in the build. How
do we organize the dependencies from other Git repositories moving forward?