Add --exclude flag and change --opaque

[Nadrieril]

This complements --include and --opaque: --opaque means "translate the signature of the item but not its contents". When even the signature is something we can't handle, we can now use --exclude to skip its translation entirely.

[sonmarcho]

I actually think --opaque would make more sense than --exclude, and --exclude should have the current meaning of --hide. What do you think?

[Nadrieril]

Yeah that would make more sense you're right