Grunt doc generation task

Adding a grunt task so that documentation can be generated from the command line with `grunt jsdoc`. This helps being able to do documentation generation in a portable way since all the options that would be applied are stored in Gruntfile.js.

I've generated the docs once again using the grunt task, and here is a summary of the differences:

*  downgrades from JSDoc 3.3.0-dev to 3.2.2
*  lots of whitespace changes