Update less dependency to current version 2.3.x
Update version of project to make it easy to depend on it
Add dependency on therubyracer or therubyrhino as per the pull request from https://github.com/klanning/guard-less/commit/a31abdefe87fde2a0f01ef0749f21a83a9ed08ca
Merge pull request #14 from dwt/master

Updated requirement of less to allow usage of advanced features.