Add search

[ArmorDarks]

We definitely should go with client-side search, but yet to decide with which one.

Candidates:

• http://lunrjs.com/

  https://github.com/jediq/grunt-lunr-index-generator https://github.com/assemble/grunt-assemble-lunr

  Some random tutorial: http://jekyll.tips/jekyll-casts/jekyll-search-using-lunr-js/