Corrections to comparison with Bootstrap

* Flex Video: http://getbootstrap.com/components/#responsive-embed
* NPM: https://www.npmjs.org/package/bootstrap
* Ruby Gems: http://rubygems.org/gems/bootstrap-sass
* Composer: https://github.com/twbs/bootstrap/blob/master/composer.json
Merge pull request #61 from cvrebert/master

Corrections to comparison with Bootstrap