Split Document into Document, TextDocument.
Added ability to register DocumentFactory objects with server.
Initial run at splitting Content from Document
Make Content.controller public
Re-merged Document/Content
Eliminate Connection's knowledge of Messages
Replaced DocumentFactory with DocumentType.
DocType now implements Operation transformation.
Prune dead code.
Add DocumentType-specific Message parsing.
Re-packaged Text document type into 'text' library.
DocType returns MessageFactories, Transforms rather than applies them
directly.
Eliminated TransformType.
Clean up type warnings on Connection implementations.
Cleanup: use docType.id in registerDocType rather than param value.
Indentation.
Code convention fix CONST_CASE->camelCase.
Merge branch 'multi-doctype'

Conflicts:
	lib/client/connection.dart
	lib/server/connection.dart