Refactor ctagsplugin.py

- Rename variables to be consistent
Add tests for ctagsplugin.py

- Add 'mock'-style class for sublime and sublimeplugin imports
- Add test cases for ctagsplugin.py functions
- Minor refactoring of files
Add additional unit tests for ctagsplugin.py

- Add additional unit tests
- Refactor some methods for improved clarity
- Replace unecessary creation of real files and directories in some
  tests with string representing file and directory paths
Refactor ctagsplugin.py

- Rename functions and function parameters for consistency
- Update unit tests with renamed functions/function parameters
Refactor ctagsplugin.py

- Refactor get_common_ancestor_folder function
Update ctags.py with sphinx-style docstrings
Modify settings function

- Remove unnecessary reading of settings from general settings
- Add docstrings
Add additional documentation
Split JumpToDefinition function

- Split JumpToDefinition function due to apparent lack of support for
  args in Sublime Text 3
Remove dead code from test_ctags.py
Updated test_ctags.py for Python3
Update test_ctagsplugin.py for Python3