Fix compiler warnings.
Refactor; add ui module to hide SDL calls.

Only done video so far; events, timers to come
Refactoring; add simple event queue to ui
SDL init only video and timer subsystems, not all
Add _t suffix to ui types.
Refactoring; add simple timers to ui
Remove straggling icons.h.
Add a few missing _t suffixes.
Silence make clean if there's nothing to do.