Merge pull request #1 from arteymix/3.2/develop

3.2/develop
Using a single less compiler (more efficient on memory and cpu usage).
Using the css compressor from the lessphp instead of using the css
compressor from Minify_CSS.
It is useless for Minify_Less to inherit from Minify_Css since it has
its own compressor (that I suppose more efficient).
Added a test for less.
Added some defined("SYSPATH") for security.
Added documentation and a license (GPLv3) for the work, it is the same
as lessphp license. Also refeering the website and the author of lessphp.
Merge branch '3.2/develop' of https://github.com/ryross/minify into 3.2/develop