Moving the `captured_output` function to own file.
Adding homegrown unit testing helper classes `Stub` and `Mock`.
The issue is that the unittest.mock was added in Python 3.3 and we need to run on Python 2.7. `Stub` and `Mock` were organically developed as minimal implementations to support the common testing patterns used on the original branch, but since I’m rewriting the commit history to provide an easily digestible narrative, it makes sense to introduce them here in one step as a custom unit testing library.
Moved result formatting methods from `PerformanceTestResult` and `ResultComparison` to `ReportFormatter`, in order to free PTR to take more computational responsibilities in the future.
Coverage at 99% according to coverage.py
* `compare_perf_tests.py` now always outputs the same format to stdout as is written to `--output` file
* Added integration test for the main() function
* Added tests for console output (and suppressed it leaking during testing)
* Fixed file name in test’s file header
compare_perf_test.py is now covered with unit tests and public methods are documented in the implementation.
Minor refactoring to better conform to Python conventions:
* classes declared in new style
* proper private method prefix of single underscore
* replacing map with list comprehension where it was clearer
Unit test are executed as part of validation-test.
.gitignore was modified to ignore .coverage and htmlcov artifacts generated by the coverage.py package
