Configuration file

Where poly-crap finds .poly-crap.toml, how it merges with the command line, and an example.

Poly-crap looks for .poly-crap.toml in --path, then in each parent directory, and uses the first one it finds. Unknown keys are an error, so a typo cannot silently do nothing.

The command line wins over the file, and the file over the defaults, except that exclude and allow lists are joined and a boolean is on when either side sets it. Options names the key for each flag.

languages = ["rust", "typescript", "python"]
threshold = 30.0
missing = "pessimistic"
fail-above = true
exclude = ["src/generated/**"]
allow = ["legacy::*", "vendor/**"]
sort = "file"
jobs = 4