Add exclude option in selene.toml

[captalbator]

This implements an exclude glob option in selene.toml which excludes any files matching with the globs from being linted.

[Kampfkarren]

Add it to CHANGELOG.md and to the documentation for selene.toml as well

[Kampfkarren]

Conflicts with main now

[OverHash]

Should the error! calls here use std::process:exit(1) rather than return after errorring? That would be consistent with the other logic in src/main.rs..

[Kampfkarren]

@OverHash Yeah, didn't catch it