Add compileDependencies option

Redux of last week. This is the same operations, but runs faster and is moved to an outside resource.

I have added the option `compileDepedencies`, when true this adds a partial's dependent files to the current async process. I have added sass-get-dependencies as a dependency on the package.json. Written tests and updated the documentation / Readme file.
You don't need the 2nd and 3rd callback arguments.