Updated web service testing harness for new module loading strategy.
Service invocation now automatically JSONifies the result if it is not a string.

This allows for web services to be as simple as possible - they can just return
a Python object, and it will be automatically converted to JSON; or, if they
need to do any custom conversion, that can be done in the service itself (i.e.,
for MongoDB JSON conversions to handle special fields like $date, etc.).
Testing harness now runs web services directly via tangelo.invoke_service().
Removed ner.py's dependence on json.
Removed census.py's dependence on json.
Merge branch 'issue-86'

Closes #86.