Add an _EX suffix to the light versions of colors.

While the sequences are handled by many terminals, it is not part of the
ISO ANSI standard.  Let's signify this by adding an _EX suffix to the
names.
Add tests for the light, extended colors.
Merge pull request #23 from jszakmeister/adjust-names-for-extended-colors

Add an _EX suffix to the light versions of colors.