Setup bumpversion

[webyneter]

• Create use_bumpversion cookiecutter option.
• Require bumpversion==0.5.3 locally.
• Refactor version resolution in ./docs/conf.py: Now, there's a single 'source of truth', the release variable representing 'the full version, including alpha/beta/rc tags', allowing the version to be derived dynamically from itself.
• Provide bumpversion config file pinpointing project version in ./package.json (the version attribute), ./{{cookiecutter.project_slug}}/__init__.py (the __version__ variable), and ./docs/conf.py (the release variable).

N.B. The whole point of refactoring ./docs/conf.py was indeed to faciilitate seamless version bumping.

[webyneter]

For now, bumpversion lacks full-fledged support for pre-releases (as semver prescribes). I've come up with a trivial workaround (still, not abiding to semver to the utmost extent) working in a following manner:

0.1.0 →
bumpversion pre→ 0.1.0-1.0 →
bumpversion prenum → 0.1.0-1.1 →
bumpversion prenum → 0.1.0-1.2 →
bumpversion major → 1.0.0.

[luzfcb]

Apparently, bumpversion has no active maintainer in it since 2015.
To my understanding, we should avoid using it, due to the first rule: https://github.com/pydanny/cookiecutter-django#constraints

That said, there is this fork https://github.com/c4urself/bump2version but I've never used it.

[webyneter]

@luzfcb, I see, you're right. I'm closing the PR.

[luzfcb]

I am +1 to add any actively maintained library and that does something similar to bumpversion and a minimum documentation of how to use.