Shtab

- :hammer: fix bash missing custom complete functionality (`add_argument().complete = ...`)
- :hammer: fix subcommand completion & update `examples/customcomplete.py`
- :tada: add `shtab.add_argument_to(parser, option_string)` (18)
+ option: adds `your_cli_app [--print-completion={bash,zsh}]`
+ subcommand: adds `your_cli_app completion [{bash,zsh}]`
+ handles the `print(shtab.complete(parser, shell))` & `exit(0)` logic too
- :tada: expose `SUPPORTED_SHELLS`
- :book: add & update documentation
- :mag: add tests
- :broom: misc tidy

- :tada: add `--prog` override (16)
- :tada: search curdir for modules (17 <- 12)
- :mag: add & update tests


- :hammer: fix `AssertionError` on valid choices (15 <- 14)
- :left_right_arrow: add logo (13)
- :mag: add tests
- :hammer_and_wrench: misc framework updates
+ fix & update deploy bot helpers
+ tidy setup.py

- add new custom-complete API `add_argument().complete = shtab.FILE or shtab.DIR or dict(zsh=..., bash=...)` (9)
+ support `bash`
+ support `zsh`
- update documentation
+ update `README.rst`
+ update `examples/*.py`
+ remove all mention of old `choices` API
- misc CI framework updates
+ fix autogenerated changelog missing info
+ fix tags not triggering CI

- add `--version`
+ `use_scm_version` to auto-detect version via `setuptools-scm` if possible
- tidy package structure
- docs: update contributing guide
- CI: add `Comment Bot` action
+ support `/tag vM.m.p SHA` comments for releasing!

- re-fix `argparse` dependency for py<2.7 and 3.0<=py<3.2 (7, 6 <- 5)