Add --exclude and --exclude-glob flags

[idofran]

Both flake8 and black have --exclude flag which works the same as --skip-glob in isort.

This is highly confusing because --skip-glob isn't a real glob, and works using fnmatch.

aliasing --exclude to --skip-glob and creating new real glob option called --exclude-glob will make isort compatible with --exclude option in other utilities and add a new glob option if anyone really meant to use glob.

In my opinion, it is best to deprecate --skip-glob and replace it completely with --exclude, however I'm not sure what is the policy here for doing it.