BaseAPIMethod abstract class and an implementation of ListCourseSections in the sections method module complete with tests.  Include mock library for tests.
PEP-8 formatting fixes
Added doc strings for tests.  Rename MockAPIMethod to StubAPIMethod in base api test file.  Added doc string describing input parameters including acceptable values for 'include' string.
Merge pull request #3 from Harvard-University-iCommons/feature/base_api_method

Feature/base api method plus ListCourseSections call.
Merge branch 'develop' into feature/create_client