Use git repo data (latest tag, current commit hash, etc) for building a version
number according PEP 440.

Features:
- Can be installed & configured through both setup.py and PEP 518's
  pyproject.toml
- Does not require to change source code of the project
- Tag-, file-, and callback-based versioning schemas are supported
- Templates for tag, dev and dirty versions are separated
- Templates support a lot of substitutions including git and environment
  information
- Well-documented