add support for bootstrap with sass

- completes part 2 of 3
- added a number of tests to make this
  process easier, including the ability to
  share tests using shared-examples.js
  module(my first node module by the way)
- support for stylus is pending. There is an
  issue with the bootstrap mixin and the
  stylus compiler. The mixin was copied
  over from Less and the syntax causes
  an error. Commenting out the entire mixins
  file from the bootstrap-stylus bower package
  fixes the issue, however, it’s also not ideal
  My suggestion would be to merge this and
  open another issue for stylus bootstrap
  support. I have the tests written and the
  implementation for the generator but the
  fact that actually using stylus won’t work
  blocks less and sass support which do work

/cc @eastridge, @ryan-roemer

@ryan-roemer, PS check out the test-creation.js
file and shared-examples.js module,
let me know your thoughts, it may require
cleanup but the shared specs are making this
process, especially with many branches in
generator control flow(like experienced in
this PR) easier. Test coverage is way higher,
but it’s possible I’ve overlooked something
as it felt far too simple to add rspec like shared
examples via a 10 line node module :P