* Plip natively uses 32-bit stereo floats. The frontend is responsible for
converting this to the system's native format.
* Somewhat buggy (wrt conversion) SDL audio implementation added.
* Test code included, free of charge!
* Moved test event loop into SdlEvent. Currently only checks for SDL_QUIT.
* Window scale and target frame rate can now be specified in the config.
* Target frame rate can now be specified on the command line.
* Implemented a format-agnostic way of plotting pixels and getting the
number of bytes per pixel.
* PlipInput can no longer be inherited.
* Added width/height getters to the video subsystem.
* Properly initialized SDL2 and added a temporary event loop (required to
get the window to appear on macOS).
* Sorted all source files into appropriately named directories.