Use exportsOverride to rename target folders

I needed to be able to easily customize target folder names in my project to follow convention that uses version numbers in folder names, so that i.e. `"jquery": "~2.1.1"` (from `bower.json`) gets installed to "js/**jquery-2.1.1**" (and not as now to "js/jquery"). This change extends `exportsOverride` configuration option with `packageName` naming convention which is run through [Handlebars](http://handlebarsjs.com/) with package's metadata (so one can install to i.e. "js/jquery-2.1.1" based on metadata of Bower packages). I also added dependencies to Q and Handlebars to make it work. You can find more details in updated Readme file.