Make Identifier show a orangish tint and PreProc different from keywords

The `Identifier` group is colored 223 (`NavajoWhite1`), and `PreProc`
209 (Salmon1).  The former makes vim help text much more readable, while
the latter helps with shell programming.
Merge pull request #2 from congma/master

Make Identifier show a orangish tint and PreProc different from keywords