Added filter by tags feature

Implemented filter by tags with permalinkable urls.
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). 

![Sample Screenshot](http://s29.postimg.org/l9jj41uvb/sample_filters.png)