Bugfix create_pdfs stdout writing with no info

* When create_pdfs is run without a long org or long_course configured,
  their values were None, which would cause the stdout report writer to
  blow up. This defaults them to empty string, which can be printed
  nicely.

* Change the randomized title assignment flag to be -T which is more
  mnemonic

* Reassign the -R flag to generate no report at all, even one to stdout
Merge pull request #35 from edx/jrbl/bugfix_stdout_report

Bugfix create_pdfs stdout writing with no info
Ignore .coverage
Merge pull request #36 from stvstnfrd/coverage

Ignore .coverage
Make credits configurable on Stanford CME

* Assumes cert_data stanza now has additional "CREDITS" subdict, with a
  key "COUNT" and a key "TYPE". These are interpolated directly onto the
  certificate.

* Adds documentation to the CME renderer explaining the various
  cert-data configuration parameters which it respects. Adds
  documentation to the README explaining that internationalization
  should be handled by forking.