Tcms-api

**WARNING:** contains backwards incompatible changes!

- Compatible with Kiwi TCMS v9.0 or later
- Method ``Backend.build_id()`` doesn't receive ``product_id`` as firsts
parameter anymore! Related to https://github.com/kiwitcms/Kiwi/issues/246

- Use a sub-package to install gssapi, see installation instructions

- Fix ``super()`` call in ``CookieTransport`` class to make this package
compatible with Python 3.8 (Václav Klikar)

- Add instructions how to install `gssapi` because they don't ship binary packages on Linux
- Provide `plugin_helpers.Backend.get_statuses_by_weight()` and fall-back to it if TestExecutionStatus can't be found by name. This is to be used by Kiwi TCMS plugins (Bryan Mutai)

- Use ``gssapi`` library for kerberos communications on both Linux and Windows
- Requires MIT Kerberos for Windows, see installation instructions

This version adds additional methods and functionality that can be used
by Kiwi TCMS plugins written in Python.

- Modify ``plugin_helpers.Backend.test_case_get_or_create()`` to return
tuple (dict, bool). WARNING: this will break existing plugins
- ``plugin_helpers.Backend`` will use ``TCMS_PLAN_ID`` environment variable
if specified. This allows the user to select an existing TestPlan to save
new results into. Fixes
`Issue 5 <https://github.com/kiwitcms/tcms-api/issues/5>`_
- Add ``plugin_helpers.Backend.finish_test_run()`` which may be
called by plugins to indicate that a TestRun has been finished
- Add ``plugin_helpers.Backend.default_tester_id()`` and update
``TestExecution.tested_by`` when changing status
- Use ``default_tester_id()`` when creating a new TestRun
- When creating new test run always set TR.manager := TP.author
and make sure that ``TestPlan.create()`` will also specify author