Add html2js task

This implements the html2js task that is performed by the [grunt-html2js](https://github.com/karlgoldstein/grunt-html2js) plugin in a Grunt build. Useful for AngularJS applications that wish to bundle their templates as Javascript files for nicer caching etc.

Implements most options, but not any dynamic stuff, so no processing of html files as templates or jade template processing at this point.

Implements #95