fix ci configuration

[bmos]

Updated CircleCI configuration for better maintainability and more complete testing of supported python versions.

Highlights

• all tests now pass on all supported versions of python
• .egg files are no longer created/uploaded to pypi as it was rejecting them
• ci cache keys now includes checksum of tests/requirements-syntax.txt
• tests now only run if syntax checks pass
• docs now runs as separate workflow from all the rest
• no longer testing python 3.4 as it's not available on circleci
• the only changes to program + test code are formatting / noqa comments to get checks passing

[coveralls]

coverage: 91.654% (-0.01%) from 91.667%
when pulling 0f02dc8 on bmos:patch-2
into dc07328 on pahaz:master.