Refactored tests into smaller modules.
Converted all unittest asserts to plain, pytest-powered asserts.
Moved fixture constants to tests.fixtures.
Switched to @pytest.mark.skipif.
Cleanup

XX
Finished pytest migration.
Added CONTRIBUTING.rst.
Added tests for --debug and --help.
Added docstrings for utilities in `tests.__init__`.
More tests.
Added Python 2.6 compatible OrderedDict

To preserver ordr of headers, parameters, etc.