Regexp pattern accepted by --exclude option

[jimbrowne]

This builds on the patch from @NotDaveLane; I've needed to use regexps for excluding files rather than just simple substrings.

Probably want to pull in the simplification from @victorpoluceno as well.

[seedifferently]

@jimbrowne thanks for this...an --exclude arg has been planned for some time but my life has not allowed space for work on this project. I will add it to my list of "future TODOs."

[etiennesky]

the Regexp patterns are different from those used in rsync right?

which simplification from @victorpoluceno are you referring to?

[etiennesky]

this is probably error-prone as it matches all directories that start with (but do not match exactly) the given exclude pattern