- Suppress (some more) warnings when doing `brew install --quiet`
- Clarify `man brew` output that we don't suppress all warnings
  for all commands with `--quiet`

While I was doing this I noticed references to the (soon to be
deprecated) `brew switch` so:
- remove these references in `install` output
- remove a reference in the documentation
- add a comment to remind me to deprecate `brew diy`, too

Fixes #9179

Fix `-1` and other flags so they're handled correctly with casks. Use
the "right" exceptions for declaring invalid combinations and change
their parent class so that `--help` is printed nicely too.

Fixes #9033

The way we currently handle @-versioned formulae linking is pretty
labourius:
- it requires extensive use of `link_overwrite` to avoid the `link`
  stage failing on certain install/upgrade scenarios
- we teach people to use `brew link --force` whenever they wish to
  link a versioned formulae when it's pretty obvious what's expected
  in that situation

Instead, let's:
- automatically unlink other versioned formulae when linking a
  versioned formula (either through `brew link` or `install`/`upgrade`
  /`reinstall`)
- notify the user what we've done (with the same messaging as if
  they had run `brew link` manually)

This hasn't been accurate since #1860 and #5650.

cmd/list.rb: --formula, --cask as default TTY:

cmd/list.rb: proper deprecated message on non TTY outputs

update manpage

update zsh completion

updated manpages/brew.1

update tests

return list_casks

list_spec.rb: not output to stderr

GitHub has requested we request our usage of shallow clones. As a
result:

- do default to shallow clones on CI
- do not do --shallow-since when setting up new repositories in
  `brew update`
- do not support shallow clones of homebrew-core at all

We may consider in future unshallowing all clones unconditionally.

Add an opt-out of this behaviour.

to GitHub Releases

This API authentication path will be disabled on Nov 13 2020.

- This was suggested in https://github.com/Homebrew/brew/pull/8741#discussion_r490949486.