fix #431 - directory not ignored with negative pattern

[deadc0de6]

fix #431

The issue lies in the fact we do not ignore directories when there is any negative ignore pattern defined. This is to force the caller to enter the directory and evaluate any potential negative ignore pattern inside it.

See https://github.com/deadc0de6/dotdrop/blob/master/dotdrop/utils.py#L307

• [x] discard empty directory
• [x] static instead of recursive search (construct diff from static tree of both sides and then compare)
• [ ] see if the same applies to the other commands
  • [x] compare
  • [ ] install
  • [ ] update
  • [ ] import