Whitelist PHP formulas in shadowed header audit check

Revert "cc: always filter flags on deps."

keg: use resolved_path not realpath.

This guards against this being a non-symlink in which case it will fail.

Fix abv and prefix_linked?

Use docs.brew.sh links.

formula: correct grammar in comments

docs: fix titles on docs.brew.sh

licenses: update copyright year

otherwise whenever prefix is unversioned, prefix_Linked will be false

versioned prefix is a directory, but unversioned is a symlink, so
realpath it before computing abv

tests: remove temporary tab homebrew_version override

Cleanup documentation site

GitHub now nicely generates a documentation site for us at
http://brew.sh/brew based on our docs folder. Optimise the output of
this and the GitHub docs directory for readability and the various user
groupings.

audit: deprecate env :std/:userpaths for strict.

This had to be added in #1750 to work around special-casing for tabs
generated with Homebrew versions < 1.1.6. Now that 1.1.6 is the current
version, we can remove this hack.

This should apply only for new formulae but we should start gradually
phasing it out for older ones too.

formula: make prefix usually return opt_prefix.

Deprecate Homebrew/versions, Homebrew/devel-only.

General documentation updates.

See https://github.com/Homebrew/brew/pull/1771#issuecomment-270143292.

See https://github.com/Homebrew/brew/pull/1771#issuecomment-270179479.

Don't use Homebrew/versions in a test and remove them both from the
OFFICIAL_TAPS list (i.e. `brew search`).

update-report: handle homebrew/versions imports.

Mostly related to the newer ways we’re handling versions and the
incoming deprecation of devel-only, head-only and versions.

Disallow file separator in version strings.

Imports from homebrew/versions are migrated from that tap and then
renamed immediately when they hit homebrew/core. This did not trigger
our previous rename detection so address these to improve the output and
handle migration correctly.

bottles: --force-bottle feigns or_later.

When reproducing issues with software that hasn’t been bottled yet on
your version of macOS it can sometimes be helpful to use `or_later`
bottle functionality i.e. just use the bottle for the latest version of
macOS available. This maps well to the existing `--force-bottle`
argument so it will now act as if the latest bottle has a `or_later`
ending.