Generate zsh completion script automatically

[Freed-Wu]

Fix #503

Modified from https://github.com/ytdl-org/youtube-dl/tree/master/devscripts

/usr/share/zsh/site-functions/_ptpython

#compdef ptpython ptipython

_arguments -s -S \
  '(- *)'{-h,--help}'[show this help message and exit]:str' \
  --vi'[Enable Vi key bindings]' \
  {-i,--interactive}'[Start interactive shell after executing this file.]' \
  --light-bg'[Run on a light background (use dark colors for text).]' \
  --dark-bg'[Run on a dark background (use light colors for text).]' \
  --config-file'[Location of configuration file.]:file:_files' \
  --history-file'[Location of history file.]:file:_files' \
  '(- *)'{-V,--version}'[show program'\''s version number and exit]:str' \
  '*:args:_files'

❯ ptpython -<Tab>
option
--config-file    Location of configuration file.
--dark-bg        Run on a dark background (use light colors for text).
--help           show this help message and exit
--history-file   Location of history file.
-h               show this help message and exit
--interactive    Start interactive shell after executing this file.
-i               Start interactive shell after executing this file.
--light-bg       Run on a light background (use dark colors for text).
--version        show program's version number and exit
--vi             Enable Vi key bindings
-V               show program's version number and exit
❯ ptpython --config-file <Tab>
file
CHANGELOG       examples/       MANIFEST.in     ptpython/       README.rst      setup.cfg       tests/
docs/           LICENSE         mypy.ini        pyproject.toml  scripts/        setup.py

[Freed-Wu]

#509