v1.0-rc3

Mostly refactors.

Changelog:

• breaking: stop sourcing files from ~/.config/qutebrowser/conf.d/
  • this was undocumented, nonstandard, and didn't work as well as it could
• switch to pyproject.toml
• hopefully use the right qutebrowser dirs on Windows
• choose: add qutebrowser menu item for the main qutebrowser profile
• added -C argument to support referencing qutebrowser configs other than the one in ~/.config
• added click-generated completions for bash and zsh
• added option support to fish completions
• removed --create from qbpm launch
• make generated .desktop files match qutebrowser's more closely

Full Changelog: 1.0-rc2...1.0-rc3