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.

Co-Authored-By: Mike McQuaid <mike@mikemcquaid.com>

Also, while we're here, `rsync` and `git` are not acronyms.

- Use Ruby attribute arguments.
- Fix use of `full_clone` in `cmd/tap` to be on by default.
- Remove unnecessary argument in test.

This makes `Tap` consistent with what the installer is doing.

Generally shallow clones get slower and slower (and more and more
pointless) the more they are fetched so don't make sense for our
use-case.

Keep the option around anyway because it's useful for integration tests.

Use active voice when applicable, better verbs & adjectives, preposition usage, proper tense, etc.

- remove odisabled
- move odeprecated to odisabled

Replace <var> tags with markup for italicized monospaced text in Markdown.
This requires the source to not combine bracketed and backticked text.

- Turn more old `odeprecated` into `odisabled`
- Remove more old `odisabled`
- Remove code for older Ruby versions

Fix various circular requirements, method redefinitions, etc.

There are none remaining. We don’t want PHP to get the deprecated
messages until all formulae have been deleted so that will be in a
later PR.

Deprecate more methods. Internal APIs have been verified to be unused
elsewhere and removed. External APIs have had deprecation methods added.
Existing deprecations have been either upgraded to produce warnings or
no longer deprecated and the reasoning documented.

Taps can include completion scripts for external commands under
`completions/bash`, `completions/fish`, or `completions/zsh`. `brew tap`
will automatically install these into the correct directories during
install.

You need a non-shallow clone to push branches upstream so if you often
tap and untap taps (e.g. `homebrew/boneyard`) then you need to remember
to manually `fetch -unshallow`.

Makes `tap` re-runnable and unshallows when requested with `--full`.
Tapping with a different URL raises an exception.

The homebrew/core tap cannot be untapped with `untap` so running
`brew tap --full homebrew/core` is now a built-in way to get a full
clone of this tap without resorting to workarounds.

Closes #17.

Signed-off-by: ilovezfs <ilovezfs@icloud.com>

We don't need to migrate the tapped formulae from symlink-based to
directory-based structure any more.

Instead, we add core tap install check for `brew update-report` which
will be invoked by `brew update`.