Add unlicensed crate to exceptions

[f-squirrel]

I would like to have an option to add an unlicensed crate to exceptions.
E.g.:

exceptions = [
    # Each entry is the crate and version constraint, and its specific allow
    # list
    #{ allow = ["Zlib"], name = "adler32", version = "*" },
    { allow = ["unlicensed"], name = "my _crate", version = "*" },
]

[Jake-Shadle]

I don't think there is a need for this, crates without license are incredibly rare, and the clarify mechanism can be used to specify license information for the crate, even if might be a lie while a PR or issue is worked through by the owner of that crate.

[extrawurst]

That solution probably deserves a mention in the docs

[Jake-Shadle]

I'm prepping a release I am updating the docs as part of that.