From the 8.1 Xcode Beta:
```
There is no Command Line Tools (OS X 10.11) for Xcode 8 package. Xcode 8 contains
SDKs that are incompatible with earlier toolchains. Developers who want to make
use of the Xcode 8 SDKs from the command line must choose the SDK with `xcode-select`.
Developers on OS X El Capitan who have installed versions of the Command Line Tools
(OS X 10.11) for Xcode 8 Beta should install Command Line Tools (OS X 10.11)
for Xcode 7.3.1.
```

Thanks Apple.

formula: help CMake with 10.12 SDK on 10.11

Use git describe to get the HOMEBREW_VERSION.

update.sh: don't print "checkout branch" message.

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

Ask for `sudo` when moving Caskroom.

It’ll only get printed for people getting updated to tags now and these
are people who haven’t run a `dev-cmd` so we want to air on the side of
telling them less stuff that will confuse them and assume people who
have manually made another `git` branch will know how to get back to it.

For tagged commits produces the output:
- `1.0.1`

For untagged commits with a dirty tree produces the output:
- `1.0.1-19-g23efbc5-dirty`

Performance:
```
git describe --tags --dirty 2> /dev/null
0.07s user 0.01s system 96% cpu 0.086 total
```

This means we can tag any commit without needing to manually remember
to bump the revision every time.

Delete old cctools-based relocation code.

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

Disable check for $HOMEBREW_NO_RUBY_MACHO now that no alternative exists.