Adds feature to exclude files from source

[nickschuch]

Adds support to exclude paths using globbing.

What would be the next steps for merging? Where would you like me to contribute tests?

[at-wat]

@nickschuch Thank you for your PR!

I think it's better to make the exclude rule definition more generic by specifying filter func (path string) bool instead of a pattern string, so that users can use not only glob but regexp, complete match and any other custom filter.

What would be the next steps for merging? Where would you like me to contribute tests?

Yes! Please add some tests to ensure it works as expected and won't be broken in future.