Added option to skip errors

Hey Yuan.

I've found that when using 'find' where there are directories with permissions limiting the user, it throws an error, and I wanted to be able to avoid those directories and just keep on 'finding'...

I've created a patch, and I'll appreciate your review.
If anything is missing or wrong, I'd be happy to resolve it.

(I've been using 'find' for this: https://github.com/danyshaanan/git-repos )

Thanks,
Dany.