Add Constant Highlighting

Add handling of `font-lock-constant-face` to handle things like `NULL` and
`true` in c-mode. The default colors for these are silly.
Transition Dorsey to Deftheme Format

Updated the theme. Added highlighting of constants to the theme too. Changed the
colours of the text in the mode-line and mode-line-inactive around as it didn't
seem to make any sense.
Update Installation Script

Add Dorsey to Installation script.
Align Colours
Merge pull request #3 from iwillspeak/dorsey-added

Dorsey Theme