Enhancement: Unify exclude/include

[pykong]

The readme states:

# Shell-style patterns files/folders that must not be copied.
_exclude:
  - "*.bar"
  - ".git"
  - ".git/*"

# Shell-style patterns files/folders that *must be* copied, even if
# they are in the exclude list
_include:
  - "foo.bar"

Probably it would be better to just have a single setting exclude but enhance it with a negating syntax that would allow to specify paths to include nonetheless. Maybe we could take gitignores syntax as an inspiration here. A leading ! will make a path non-ignored. See: https://git-scm.com/docs/gitignore#_examples

I have found the following libraries which mplement the kind of pattern matching we are looking for:

• https://github.com/cpburnz/python-path-specification
• https://github.com/tsileo/dirtools
• https://github.com/untzag/gitsieve

[pykong]

@yajo I can implement this.
The package pathspec works like a breeze. :-)
However, it does not yet feature unicode support. Hence files like ñana.txt would never get excluded, because of their special char.

I assume for you, as well as other Spanish speaking users such unicode support is absolutely vital?

EDIT: It seems I can make it work anyway. The unicode issues might stem from somewhere outside pathspec, namely I have messed up the tests because my editor does not properly render those symbols.

[yajo]

I like the idea of this PR, and also using a good lib that handles this transparently, but yes it should support unicode. Otherwise it's a regression.

Another idea is to use regexps, but that's maybe not as comfortable as a proper glob system. pre-commit uses regexs, in case it matters.