Make EnumSetUtil efficient but unsafe
Remove sdl::util::from_bytes (because it's useless for now)
Include util.rs into sdl module

Fix of d8df69d5ed2132196b510f644742d3dcf7b00ab5
Add impl_clike! and export macros
Replace InitFlagSet to EnumSet<InitFlag>
Add keycode.rs and scancode.rs
Fix keycode.rs to avoid ICE
Add wrap_keyevent()
Add lesson4_ex.rs