add option to import highlighted text

If the --highlights flag is passed to codeq it will import a
:code/highlight attribute along with each text segment it imports.
It uses the Pygments highlighter to do this, and outputs to HTML.
The pygmentize script must be on the command line, or in the directory
the jar is being excecuted.  Highlighting support is independent of the
analyzer; it should work with future analyzers as long as they import
the :code/text attribute.