Lemoncheesecake

- **API**: `load_report()` and `Report` are now public and documented
(see http://docs.lemoncheesecake.io/en/latest/report.html)
- **under the hood**: minor improvements to `Report` and related classes before making them public
- Add official support for Python 3.9

- Make fixture evaluation order more intuitive
- Fix 'lcc report -s' displaying bad statistics when filtering arguments are used (regression introduced in 1.2.1)

- **API**: add ``load_fixtures_from_module``
- **under the hood**: add ``Report.build_message`` (refactored from Slack reporting backend)

- The `project.py` file is now optional (and `lcc bootstrap` command deprecated)
- The `project_dir` argument for `Project` is now optional
- The `description` argument for `lcc.test()` and `lcc.suite()` decorators is now optional
- The `SUITE` variable in module-suite is now optional
- The `*.py` companion file for a suite-directory is now optional
- **doc**: "Writing tests" and "Project customization" chapters have been overhauled

- Fix `setup_suite`, `teardown_suite` and fixtures being executed even if the related suites/tests are disabled (see 16)
- Fix suite's modules not properly sorted alphabetically by default
- Fix undesired symbols import while doing the wildcard import `from lemoncheesecake.matching import *`
- `any_of()` and `all_of()` matchers: make the description single line when suited
- `is_none()` matcher: improve matcher's description
- **under the hood**: refactor and add new tests on command `lcc run`

- **lcc run**: --exit-error-on-failure also returns a non-zero exit code on any failure in a setup/teardown result (see 15)