Some functions which applies to scoped tags in general moved from TaskTag to Task model.
Also, some stylish and whitespace changes and docstrings added.
Coverage: code coverage testing for Python
Coverage.py is a Python module that measures code coverage during test execution.
It uses the code analysis tools and tracing hooks provided in the Python standard
library to determine which lines are executable, and which have been executed.
For more information, see http://nedbatchelder.com/code/modules/coverage.html