Switch color lookup to a list instead of dict

This will hopefully allow switching to higher number of colors easier.
Add 256 color mode

Just draw background in 256 color mode.
Simplify color conversion code
Make pixels 2 characters wide

Hide Cursor.
Simplify color init code.
Round instead of Ceil

Extremely low intensitys are tend towards black now.
Merge pull request #2 from tgerdes/master

256 color mode, thank you, tgerdes.