Minor change
Merge branch 'master' of github.com:plain-vanilla-games/schematics

* 'master' of github.com:plain-vanilla-games/schematics:
  source exception name is prettier now, but that is a relatively unholy number of underscores in one line of code
  fixed test, renamed it to reflect SerializableError, added type(source_exception) into str repr for SerializableError
  specifically grabbing exceptions that occur during serialization of @serializable methods, and raising SerializableError(source_exception) to make tracking them down easier
  Removing unused datastructs
  Change Model iterator to conform to dict format
  Make errors inherit from builtin exceptions
  Add simple testcase
  Add URLType based on dictshield URLField
Serializable support roles