Clean up old code and comments.
Fixed incorrect horse.
Fixed torch.
Make sure division results in float.
Split cart into separate models.
Use std::chrono for higher resolution.
Revert "Reduce input delay even further."

This reverts commit dad17375a1fab243ce7663104b11f98490bd32b7.

We can't do input processing in a frame listener, since it can lead to
other parts of the code deleting frame listeners, which will then result
in segfaults.
Process input and do UI rendering more efficient.

We'll do input polling and UI rendering while waiting for queued render
commands to finish, before swapping buffers. This should make for a more
responsive UI.
Clean up some SDL includes.