Honestly, I'm not sure how the last commit worked; the timer in
enemy.cpp wasn't being initialized. Bizarre. I don't want to know,
actually. Anyway, now the game has a "standard" framerate, and SDL_Delay
is called to wait long enough to meet that standard framerate. Enemies
will always assume STD_MS_PER_FRAME clicks have passed. This means that
if execution is slow, the enemy movement logic won't be slowed; only the
rendering will be slowed. I will change this in the future. See the
TODO in gui.cpp for more information.