Update yardoc for Utils.find_adapter
Fix utils method that was not a module method (find_adapter).
Cleanup tests (comments, blank lines, debugger).
(refactor) Make AstTransformer use Utils class to find adapter.

Finding an adapter should be in one place only.
Add documentation adapter.

The intent is that the parser associates documentation with the model
via this adapter. A doc(factory, doc_string) method is available in the
parser, as well as a Factory.doc= doc_string method.
Add concat, append operations (+, <<) for array, and merge (+) hash.

This is good because it is otherwise very difficult to perform
typical data transformations (without these operations you can
filter, map, and reduce to one - or jump through hoops trying to write
a reduction that appends.