gpg: add GnuPG series 2.1.x to supported versions

link: tell users of `brew link --force` about opt.

missing_formula: warn when git-log takes very long

If people are force-linking keg-only things they should probably be told
that they can add the opt prefix to their PATH instead.

man: generate Markdown man page.

cd tap-new: fix symlink creation.

The existing `brew.1.html` wasn't particularly pleasant to read and
given everything else in `docs/` is a Markdown file it makes sense to
generate a post-processed Markdown file that can in turn be used by
Jekyll to generate a nicely themed HTML file.

Ensure the full HOMEBREW_TAP_DIR path is created before deleting and
creating the symlink for it. This ensures that non-`homebrew` taps will
have the necessary username/organisation folder created.

Fixes #2378.

update-report: check migration symlinks.

Check if `HOMEBREW_CELLAR/old_name` is a symlink. If so, it's already
been migrated so can be skipped.

tests: unset HOMEBREW_TEMP

Hint at new location of migrated formulae

Setting `HOMEBREW_TEMP` env. var [currently] breaks tests (`brew
tests`). Although this behavior looks like a bug, the solution is
straightforward: unset `HOMEBREW_TEMP`.

formula_installer: need up to date requirement formulae.

audit: check system dupe deps on new formulae.

audit: deprecate depends_on :tex.

update-report: migrate all formulae every time.

update-report: migrated formulae were not deleted.

These methods belong together so combine them in a single class to
provide a simpler API.

This will allow extending this class so it can be used by more than
just blacklisting.

This wasn’t adapted to the new, multiple repository world.

This makes it easier to turn an arbitrary path into a tap path.

Partial implementation of
https://github.com/Homebrew/brew-evolution/pull/15, along with the ability to
search for deleted formulae in git history (inspired by #1996) which is not
described in the proposal.

See also: #1371.

Unmigrated formulae cause hard-to-debug issues and relying on detection
on Git alone is faster but not comprehensive. Instead, iterate through
renamed, installed formulae every time and migrate them.

Closes #1770.

The taps they were migrated to are auto-tapped if not already tapped
anyway so don't show them as deleted to avoid confusion.

Fixes https://github.com/Homebrew/homebrew-core/issues/10338

.

Closes #2287.

Signed-off-by: Alex Dunn <dunn.alex@gmail.com>

This has known issues with our `ghostscript` formula, we can't test it
on CI and is a ludicrously heavy dependency that in many cases can be
avoided by upstream providing prebuilt documentation.

Provide a gentle nudge to users to check if these dependencies are
definitely required.

docs: grammar edits, sentence-case secondary headings

Also changes some heading levels so only one primary
heading appears per page.

audit: online - limit download time based on HTTPS determination

Fix small typos in How-to-Create-and-Maintain-a-Tap.md