Initial import of chktex, from Marc Recht via pkgsrc-wip.

Initial import of chktex, from Marc Recht via pkgsrc-wip.
This program has been written in frustration because some constructs in LaTeX
are sometimes non-intuitive, and easy to forget. It is _not_ a replacement
for the built-in checker in LaTeX; however it catches some typographic errors
LaTeX oversees. In other words, it is Lint for LaTeX. Filters are also
provided for checking the LaTeX parts of CWEB documents.