Setuptools-scm

- introduce pre-commit and use black
- print the origin module to help testing
- switch to src layout (breaking change)
- no longer alias tag and parsed_version in order to support
understanding a version parse failure
- require parse results to be ScmVersion or None (breaking change)
- fix 266 by requiring the prefix word to be a word again (breaking
change as the bug allowed arbitrary prefixes while the original
feature only allowed words\")
- introduce an internal config object to allow the configuration for
tag parsing and prefixes (thanks to \punkadiddle for introducing it
and passing it through)

- enhance docs for sphinx usage
- add symlink support to file finder for git 247 (thanks Stéphane
Bidoul)
- enhance tests handling win32 (thanks Stéphane Bidoul)

- fix 237 - correct imports in code examples
- improve mercurial commit detection (thanks Aaron)
- breaking change: remove support for setuptools before parsed
versions
- reintroduce manifest as the travis deploy can\'t use the file finder
- reconfigure flake8 for future compatibility with black
- introduce support for branch name in version metadata and support a
opt-in simplified semver version scheme

- fix regression in git support - use a function to ensure it works in
egg installed mode

- actually fail if file finding fails in order to see broken setups
instead of generating broken dists

(thanks Mehdi ABAAKOUK for both)

- fix regression in handling git export ignores (thanks Mehdi
ABAAKOUK)

- fix regression in support for old setuptools versions (thanks Marco
Clemencic)