Add executable to sass_builder

[daniel-v]

It is tiresome to add a builder to every package in a larger project to compile sass files, the builder should support such use-cases.

• It should be invokable from command line via sass-builder command once activated as a global package.
• It will look for the configuration file sass_builder.yaml in the directory it is being executed in ( Add config reader #5 )
• Optionally look for config files recursively in the directory structure