Bumped version number to v4.0.0pre
Regenerated Python code using updated Thrift schema
Bumped version # down to v3.6.0pre, based on feedback from Max
Updated validation code for Concrete schema v3.6.0
Updated Concrete example file generated from Serif
Test suite now passes for Concrete schema v3.6.0
Updated annotate_example.py script for Concrete schema v3.6.0
Added unit test that calls concrete.util.add_references_to_communication()
Updated add_references_to_communication() for Concrete schema v3.6.0
Updated concrete_dump.py for Concrete schema v3.6.0
Added communication_service to package
Added guard condition to check for sections without a sentenceList.

Addresses #5
Added *more* guard conditions to check for sections without a sentenceList.

Every attempt to iterate over section.sentenceList in concrete-python
now has a guard condition to check if section.sentenceList exists.

This should fully address #5
get_tokentaggings_of_type() now does case-insensitive comparisons of taggingType

Addresses #6
Validation check if TokenRefSequence.textSpan fits within Sentence.textSpan
Updated to v3.7.0 of the Concrete schema