moving streamcorpus.thrift to streamcorpus-v0_3_0.thrift to avoid confusion
updating Makefile in py and scala to use the renamed main thrift file
adding default version number on StreamItem, so we can detect when a message differs
revising docs
creating StreamItem.body.external_ids
fixing "make test"
switching setup.py to use version.py and adding pytest to requirements
adding VersionMismatch to python streamcorpus and making tests to
verify which version is in use, and that exceptions get raised where
they should.
updating python thrift-generated code based on latest interface files