Added filter by tags feature

Implemented filter by tags with permalinkable urls (#32).
Libraries used: 
  * [sammy.js](http://sammyjs.org/) (compatible with IE8+ and other browsers, hope that is fine.)
  * [chosen] (http://harvesthq.github.io/chosen/)
  * [underscore.js](http://underscorejs.org/)

Added a jekyll generator `ProjectsDataGenerator` to generate json for the Projects list as a object with projects and tags properties (am new to ruby, not sure if the code is efficient enough). 
Currently rendering the projects as json inline with the HTML as the number of projects is not that high.

![Sample Screenshot](http://s29.postimg.org/l9jj41uvb/sample_filters.png)