Support extend-select in pyproject.toml

[andersk]

(I didn’t add extend-ignore since it’s the same as ignore—should we remove the --extend-ignore command line option?)

[charliermarsh]

I feel like the semantics here are off (but that they were off before with settings.ignore(&config.ignore) -- not any fault of your change). We should probably avoid calling settings.ignore(&config.ignore), since if the user provides a --ignore on the command-line, we'd want to respect that instead (not in addition). Same for extend_select.

But this can be changed separately, what you have here is an improvement in overall behavior.

[charliermarsh]

I think it's conceptually nice to have both --ignore and --extend-ignore. At least on the command-line, it's useful because you could define an ignore in the pyproject.toml, then use --extend-ignore on the command-line to augment it.