Initial placeholder
Added method to receive a map of fields by attrname, used by mapping classes
Initial work for building mappings.
Moved resources to their own file, added tests for mapping, updated fixtures to mapping test cases
Updates to mapping and exceptions
Updated method naming to match mappings file, made mappings registration consistent with resources
Added more test cases for exceptions
Completed mapping support and associated test cases
Added some mapping helpers and associated tests
Python 3 compatibility fix, TypeError no longer has a message argument.