This adds a CMake cache entry to std_cmake_args specifying that the
function clock_gettime is not available on 10.11 in order to avoid
runtime errors such as

  dyld: lazy symbol binding failed: Symbol not found: _clock_gettime

when the build system is confused by Xcode 8's weak symbols.

Other weak symbols on 10.11, which may merit the same treatment in the
future, can be found with

  grep 'weak$os10.11' MacOSX.sdk/usr/lib/system/libsystem_c.tbd

uninstall: improve pronoun for multiple version message

sandbox: tweaks

readall: do not require itself.

readme: fix maintainer link

It doesn't really need to be as tight as it is currently, certainly outside brew
you can write to here without any special privileges beside being the user,
and being so can tight can cause issues on clean systems or systems where
Xcode hasn't been used before as exposed by https://github.com/Homebrew/homebrew-core/issues/4892.

Closes https://github.com/Homebrew/homebrew-core/issues/4892.

rubocop: fix soft links targets

Add compatibility for `MacOS.release`.

When exactly two versions of a package were installed, the uninstall
message should not read "Remove them all with...", since only one
version remains.

"Remove all versions with..." is flexible enough to avoid being
interpreted as grammatically incorrect, and it still accurately
describes the general behavior of `brew uninstall --force`.

update.sh: tweak tag handling.

- Don't let the `UPSTREAM_TAG` variable bleed into future repository
  checks.
- Even if the tag branch is an ancestor of the tag ensure that it's
  forced back to the tag anyway.

readme update: it's version 1.0 already

update.sh: update to latest Homebrew/brew tag.

To test the tag update functionality allow setting
`HOMEBREW_UPDATE_TO_TAG`.

Rather than following every change on `master` let’s have non-developer
users (i.e. those who have never run a `dev-cmd` or set
`HOMEBREW_DEVELOPER`) update between tags.

This provides a fairly natural beta (the `master` branch`) and stable
(the tags) approach without restricting us to any particular way of
managing our tags.

PULL_REQUEST_TEMPLATE.md: Fix CONTRIBUTING.md link

Update: ensure tags are fetched

Update `brew-cask` man page and simplify `brew man`.

We use these for updating people who just follow tags.

Closes #1040.

Rearrange repository