Use case - Allow goymap to be used to load configuration accessible via the API

[birchb1024]

Instead of outputting a text file, add an interface to the API which allows the result of the expansions be returned to the caller as a struct, which they can use to access from inside their programs.

The main use case is using Goyamp as the config file loader. In particular, use this for the promus and shapi projects.