Repobee-junit4

As of repobee-junit4 v2.0.0, Python>=3.9 is now required.

Breaking changes
* e978f14 Update colored and drop support for Python 3.8 (112)
* 5f3315d Drop support for Python 3.6 and 3.7 (107)

Other
* a668373 Fix readthedocs config (110)
* c4473cc Tweak recurring build (106)

Bugfixes
* 396e97e Avoid trying to read directories with java suffixes (105)

Other
* b0b61d4 Add deploy workflow (for automatic deployment to PyPi)

Other
* 9e8ddf8 Set RepoBee version requirement to >=3.4.1

Breaking changes
* 08984a4 Rename rtd option in generate-rtd to make it configurable (101)
- The option previously called `--reference-tests-dir` is now called `--junit4-reference-tests-dir` to align with the same argument for the `repos clone` command
- Now picks up on the configured value of `junit4_reference_tests_dir` in the config file

Documentation
* 0443d82 Fix incorrect command example in docs (100)
* ff0bfa2 Improve generate-rtd usage docs (98)
* 8a0fec1 Documentation index page
* 2b9aa3b Add -L option to curl commands in install docs (95)
* 006a5b2 Update CLI docs (94)

Minor release with a new command: `generate-rtd`. It allows one to generate the reference tests directory from template repositories that contain the reference tests (on some branch). It's designed to be used together with [repobee-sanitizer](https://github.com/repobee/repobee-junit4).

Features
* ee17264 Allow any version of JUnit4 to be used (93)
* 7bd01e6 Add generate-rtd command (82)

Documentation
* 8b1c921 Remove module reference, fix 81
* f719df8 Update configuration docs, fix 85
* 5f5d88f Fix incomplete note in usage docs
* fdf1be0 Add documentation for generate-rtd command, fix 86
* de1c8df Replace old "master repository" terminology, fix 87

This release brings `repobee-junit4` up to date with RepoBee 3.

Breaking changes
* No longer compatible with RepoBee 2.