Add LaTeX support to the clang-highlight cli.  Introduce Numeric token type.

For a LaTeX package writer, the option "-o <output>" is handy, that's why this
option is introduced.
Add a LaTeX package together with a sample usage.

The clanghighlight.sty file is more a proof of concept than anything else,
but it should be functional.
Fix typos in documentation and add LaTeX.