I read through the docs locally and made various fixes.

Update minimum Git version.

dev-cmd/edit: simplify project view handling.

This forces the use of Homebrew's Git on El Capitan and below.
Normally I'd remove the need for this but given we're weeks away from
El Capitan being unsupported it doesn't seem worth the effort to remove
useful functionality. Instead, let's warn about an old Git and
autoinstall Homebrew's Git wherever needed.

Fixes #4818.

gitignore: general cleanup

os/mac: also update install on version bumps.

The way Homebrew is structured now there’s no need to manually
specify a few different directories here.

Remove a bunch of unneeded, old directories and generally cleanup.

I also just remembered this today so let’s add a comment reminder.

Revert "std: use HOMEBREW_ARCH env var on Linux"

 Rename `Hbc` module to `Cask`.

removes auto updates warning if greedy flag is included

std: use HOMEBREW_ARCH env var on Linux

Cask: check that the tools for quarantining are available

Use classes for instance doubles.

Rename `test/cask/cli` to `test/cask/cmd`.

Deprecate `brew cask --version`.

Remove redundant namespacing.

Add `$LOAD_PATH` for RuboCop cops.

Unlike macOS, Linux installations can be installed/deployed on a
variety of hardware. The HOMEBREW_ARCH environment variable
allows the end user to set a custom -march=... option for the
compiler. If the variable is not set, it defaults to "native".

This only applies on Linux; on macOS, behavior remains unchanged.

rust/cargo: enable caching

README: add maintainers.

Add Steven to maintainers and Dom to PLC.

scm shim: handle edge case

Since #4748 `HOMEBREW_GIT` is set by the `brew.sh`, whose value is default to be `git`.
As a result, it completely bypasses the logic of the shims/scm/git.

This fixes the issue by checking whether `HOMEBREW_GIT` and
`HOMEBREW_SVN` are set to be `git` and `svn` respectively.

Fixes #4825.

Change regex to match `filename` if header also contains `filename*`.

utils: Use JSON to marshal child errors

Refactor `Hbc::Verify`.