Less 2.4 Compatibility

Updating to the latest version of Less to enable all the new features, especially the ability to use less plugins!

Comes with some breaking changes, be sure to consult the readme for the current options.

• Upgraded to the 2.4 version of Less.
• Updated dependencies to the latest versions.
• Removed options.parser since Less is simplifying to just a render function.
• Using options.render for passing through all rendering options directly to the less rendering.
• Added postprocess.sourcemap option for modifying the sourcemap.
• Added storeSourcemap option for manipulating the sourcemap storage.
• Removed pre 0.1.x warning