Put mocks to directory structure mimicking project structure.

Use abstraction instead of using SDL dependencies.

Use our logging mechanism and remove dependency on SDL.

Use correct markup for connecting to the server.

Implement gamepad logic for macOS.

Specify final list of weapons in the game. Add additional details for
information on sprites.

Organize audio. The sfx are also rearranged.

Put input and video subsystems into their own directories.