Add support for JavaScript files

JavaScript has the same comment and string syntax as the C-like
languages, so that code is reused.
Only match filenames with the extension at the end

Previously, is(name, "h") would match "x.html" because it contains ".h".
Now, anchor the pattern to the end of the filename string.
Add HTML support including JS and CSS embeddding

With this commit codegrep will recognise *.html and *.htm files as HTML
and process HTML comments. It will also handle <script> and <style>
tags, using the appropriate comment and string formats within those.
Merge pull request #3 from mwh/master

Support JavaScript and HTML files