tests: Big push to get the tests to pass again. - Lots of fixes everywhere in the code. - Try to handle debug logging in the multiprocessing worker pool when running in pytest. Not perfect, but usable for now. - Replace all `.md` test files with `.html` since now a auto-format extension always sets the format. - Replace `out` with `outfiles` in most places since now blog archives are added to the bake output and I don't want to add expected outputs for blog archives everywhere.

---
config:
    what: not good
config_variants: [test]
in:
    pages/_index.html: 'This is {{what}}.'
    configs/test.yml: 'what: awesome'
out:
    index.html: 'This is awesome.'
---
config:
    what: not good
config_values:
    what: awesome
in:
    pages/_index.html: 'This is {{what}}.'
out:
    index.html: 'This is awesome.'