Add syntax highlighting to input generator scripts.

This patch adds a new class, GenericHighlighter, which allows
for arbitrary regexp based syntax highlighting, and extends the
input generator's scripting interface to support highlighting.

Input scripts may specify zero or more highlighting styles, and
then apply these to the input files.

The NWChem input generator script is modified to provide an example
of this new functionality.

Change-Id: Id67f306ffff00bcc594bd6d9c7a7889051cddc5f
Merge topic 'input-syntax-hilite' into master

a37d7f57 Add syntax highlighting to input generator scripts.