Another temporary tweak to bootstrap the linkml migration.

Python generator recognizes linkml: prefix to allow bootstrapping of the the linkml-model

Get any remaining fixes in before the linkml rollover

• Fixing markdown indentation issue #392
• Fixing rdf enum generation #381

Include gen-yaml as one of the command line elements

First cut at enums + several issue fixes

Enhancements and corrections to code generator including attributes keyword and case aware prefix processing

Includes fixes to markdown generator to emit all slots and include various mappings