Terminal's default FG/BG colors by default.

Should be working well, the only thing that *might* have broken is blink support though I doubt it (just couldn't test it). You'll see my first commit I tinkered with a few keys on the keyboard demo to ensure default colors got set/unset properly, and the second one I restored "normalness" on the keyboard demo, just with TB_DEFAULT instead of TB_BLACK everywhere. Also set the default FG/BG colors to TB_DEFAULT so any applications that don't *explicitly* want TB_BLACK/TB_WHITE as a colorscheme will use the terminal's default colors like it should be.

Fixes #11