better support enums, aliases, and param/result types in spec generation

[Shadow53]

I think this supersedes #219. Also resolves #270.

I'm not the best with Go, so this could probably be written better, but I figure it's a starting point. You can check the diff to see the new spec file.

Note that I chose to include *Params and *Result in the generated specification, since they (specifically *Result) are specified as the types for certain method parameters.