Adds support for LESS css

This support behaves very similar to the SASS support. It will attempt
to compile the css prior to checking for redundancies.

For c-versions of ruby, therubyracer is required. For jruby,
therubyrhino.

More information can be found at http://lesscss.org/

refs: #52, #10
Fixes semicolon parsing within a url

This is a different implementation than
828d4c801a5a9266d261ae2a770d1991cb46303b

It is also downcasing the base64 encoded data, which could cause
collision issues, but encoded images are so uncommon that I don't think
it will be a big issue. For now.

refs: #46
Fixes massive performance issue when using eql?

Not sure if it's due to constructing the array and calling #hash on it
or what, but the previous implementation is terrible on performance

refs: #42, #32
Bumping version to 1.2.0 for release