** search (crawl) for files in subdirectories

[lverdoes]

Introduces the option to search for files in subdirectories in the local filesystem, with **

[Mytherin]

Implements #5897

[Mytherin]

Thanks for the PR! Looks great. Very simple implementation (which always takes the most work :)). One comment below:

[samansmink]

@lverdoes very cool feature! I think @carlopi already talked about it with you, but we probably want to also test behaviour with symlinks. Afaik committing symlinks to git should not be an issue except for windows. An idea there is to write a test with a require notwindows which will disable the test on windows

[Mytherin]

@samansmink could you have another look?

[samansmink]

I have one more small comment, but the rest looks good :)

[Mytherin]

Thanks for the work! Looks great!