Versa pipeline improvements, & more

[uogbuji]

For release notes:

• Implement harness function versa.pipeline.transform()
• Pipeline action functions: Implement action arg to foreach()
• Pipeline action functions: Fix split arg of materialize()
• Pipeline: Implement versa.pipeline.resource_id()
• Pipeline: Fix versa.pipeline.materialize_entity()
• Pipeline action functions: Implement extra(), origin() and rel() for accessing context fields
• Pipeline action functions: Consolidate lookup() and lookup_inline() (latter is removed)
• Pipeline action functions: Implement @new-entity-hook in materialize(). Remove postprocess arg
• Consistency fixes to versa.util.resourcetypes() signature
• Pipeline: Implement versa.pipeline.create_resource_mt
• Implement versa.util.static_index()
• Fix memory models to be pickleable
• Pipeline action functions: Add unique parameter to origin()
• Pipeline action functions: Fix link()
• Pipeline action functions: Implement attach=True arg on materialize, in order to fine-tune how created resources are linked
• Implement lmdb+MessagePack driver.
• Implement diskcache driver.
• Test suite fixes