Import new brew.sh CSS changes to improve the appearance of tables and
links.

brew.sh: use OS X in user agent rather than macOS.

This matches what Safari does on macOS 10.12 and is generally what
tools like Google Analytics expect the format to be.

audit: fix audit of new formulae.

When auditing new formulae without `--new-formula` the
`audit_revision_and_version_scheme` method fails ungracefully. Instead,
set some better defaults so fewer checks are needed.

Fixes #2551.

software_spec: process macOS versions on Linux.

This module doesn't actually have any behaviour that's problematic at
runtime on Linux so we may as well use it to properly sort macOS
versions there.

formula_installer: improve install/upgrade message

If you `brew install` a formula that's already installed you get:
  Warning: ripgrep-0.5.1 already installed

If you `brew install` an outdated formula that's installed you get:
  Error: ripgrep-0.5.1 already installed. To install this version, first
  `brew unlink ripgrep`

Instead, suggest that the user should `brew upgrade` in this case. If
the formula isn't outdated use the previous message.

audit: fix use of search_tap method.

This was removed in #2540 but this call site was note updated to use
the `search_taps` method instead.

Add remote search to `brew cask search`.

xcode: update Sierra CLT version to 802.0.42

Allow forcing Homebrew GitHub organisation.

On Linux this defaults to Linuxbrew but in some cases (i.e. a Linux
machine performing uploads for Homebrew) we want to allow this to be
overridden back to the defaults.

Relies on a change incoming to `brew test-bot` to set this there.

search: use single HTTP call for tap searches.

Use GitHub's code search API to search using the filename based on the
search query. This means we only need a single HTTP call and no more
multithreading madness. This also means we're able to search everything
in the Homebrew and Caskroom organisation by default without having to
maintain a list of things to search (and not) in here.

Remove puts_hash, require pp

I wasn’t aware this existed when I created puts_hash so: may as well
remove it.

audit: audit_components method to rubocops and tests

utils: make which_editor handle editor args.

add date-based versioning

Handle cases like e.g. `EDITOR="subl -w"`.

brew: set Bintray variables.

These are set as `HOMEBREW_BINTRAY_*` and then used by the rest of
`brew` as normal.

Fix audit version_scheme and revision checks.

Another attempt at fixing `brew audit` issues around detecting
`revision` and `version_scheme` changes correctly. First done in #1754
and #2086 (reverted in #2099 and #2100).

To ease future debugging a `ph` helper has been added to print a hash
and a series of RSpec tests to verify that the `revision`,
`version_scheme` and `version` formula version audits behave as
expected.

Fixes #1731.

Fix and remove various TODOs.

Fix those that can be done so without tearing Homebrew to pieces and
remove the comments for those that can never be done.

Hide sensitive tokens from install/test/post.