Merge pull request #1 from distobj/master

Fall back to 'en' when locale unavailable (e.g. Pyspark)
Add some Versa Markdown syntax examples based on schema.org
Some code commending & doc. Rename resource type name patterns from iri to resource
DOn't include @docheader in parsed models
Major improvements to Markdown reader
Fixes to syntax for basic data typing.
Update to Python 3 support
Update markdown reader for Python 3
util.transitive_closure()
Push package to PyPI. 0.2.1 release.
Implement versa.util.all_origins
Add support for pipeline transforms. Other fixes.
Performance fix. Add Amara3-xml prereq.
Bump version.
Retool to use py.test rather than nose. Implement size and __iter__ for PG driver.
Was bitten by the RuntimeError foretold in comments. Fixed, finally.
Implement Versa pipeline context copying.
Add parse_versa_model command. Add inverse_materialize pipeline function.
Get rid of stmt cruft from RDF-think. 0.2.3 release.
Work around datachef if missing