format_desc_cop: whitelist more lowercase words

- From `homebrew-core` PR 14229, we decided to whitelist more words so
  that reordering to appease "description must start with a capital
  letter" wasn't so clunky.

rubocop: don’t allow Perl regex backrefs.

rubocop: don’t allow special global variables.

rubocop: don’t allow %x.

create: specify homebrew-core test requirements.

As requested in https://github.com/Homebrew/homebrew-core/pull/14419.

Even if shell/perl users recognise these variables the explicit versions
are significantly more readable for everyone.

Even if shell/perl users recognise these variables the English
versions are significantly more readable for everyone.

It’s confusing for non-Rubyists (and some Rubyists) and that’s a major
number of our current and future contributors.

BuildError: report options to analytics.

Add symlink for High Sierra test bottle.

Without this it's not easy to make much sense of these failures.

Revert "audit: Port audit_checksum method to rubocop and add tests"

audit: Port audit_checksum method to rubocop and add tests

analytics: remove unused analytics.

Adding shims for GCC 7

tests: cleanup tests.

formula_desc_cop: tweak some rules.

.codecov.yml: move root so files are tracked

audit: ensure curl always has at least one HTTP url.

Allow some specific lowercase words and provide an autocorrect for some
of these rules.

This makes using `HOMEBREW_CURL` significantly nicer as then the system
`curl` (that, on old versions, sucks at SSL) can download a version of
`curl` that it can build from source.

edit: tweak default editors.

brew: no issue report prompt unless autoupdating.

reinstall: remove partially installed keg.

Otherwise: you may be on an old enough version that we don't care.

We didn't end up using the `screenview` and `exception` analytics as
much as expected so let's remove them and focus on stuff that's
formula-specific.

Remove pending tests that are never run on CI (i.e. require `--online`),
remove fixtures for those tests and just make `--official-cmd-taps`
run by `--online` instead.

Add `atom` (not my editor of choice [TextMate for life!]) but widely
used enough to probably warrant it. Also, reorder based on my best
guestimates of current usage and cleanup the editor code while we're
here.