Clean up codebase from DuckTyping upgrade

[jnmclarty]

• [ ] .sourcing_map().keys()
• [ ] refactor stype and sourcing_key away from meta
• [ ] .sourcing.one()

...similar logic for munging and indexkwargs

[jnmclarty]

• [x] docs + ORM png

[jnmclarty]

• [ ] start/end can be used to test the repr obj type, pre-post cleanup.