Test runner: `joutest`

[Akuli]

I am making a test runner for Jou. It will replace runtests.sh, doctest.sh, and similar scripts in my other Jou projects.

Features:

• Philosophy: basic things should be easy, complex things should be made possible as needed, defaults should be good for basic things
• Configuration file: joutest.toml (must be in current working directory)
• Comparing # Output: hello and similar comments to actual output, like runtests.sh currently does
• Finding tests in markdown files similarly to doctest.sh
• Configurable enough to test itself with # Error: ... comments in .toml files
• Configurable enough to replace runtests.sh
• Configurable enough to replace doctest.sh

Example joutest.toml (this is everything needed for e.g. curses-klondike):

[[tests]]
files = "tests/test_*.jou

[Akuli]

I turned the issue description into a checklist that I can check as I implement more features to joutest.