Support for passing options to the base config

[jarosser06]

No description provided.

[mattjbarlow]

One thing I noticed, in the case of a Berksfile, you might want it in your base config. However, each stencil-set may have their own overrides to send to the Berksfile. I think this is similar to how you are handling metadata.rb. There should be a way to send options from the stencil-sets to files in the base config. If this already exists, then let me know.