Reorder switches as force/quiet/verbose/debug, --installed before --all, and link to SPECIFYING FORMULAE from top of page.

We’re always using the sandbox where possible now so this is just
noise for the vast majority of our users.

Also, don't delete them after that. This means that `brew postinstall`
becomes a way to easily reinstall configuration files for any formula
without needing any changes to any bottles or requiring a reinstall.

Only the top-level directories inside it. We don't want formulae writing
random junk in e.g. `/usr/local` even in `postinstall`.

If HOMEBREW_CELLAR (or HOMEBREW_PREFIX) are children of
HOMEBREW_REPOSITORY it’s important to deny write to the repository and
enable write to the Cellar/prefix afterwards.

If we have a HOMEBREW_REPOSITORY and HOMEBREW_PREFIX mismatch (now the
default) then we can block access to the whole of HOMEBREW_REPOSITORY
rather than just the HOMEBREW_LIBRARY and `.git`.

Also, flag those that we never want to be in a manpage.

Also enables sandbox for --interactive and --debug use of install
and test, using automatic retention.

Closes #66.

Signed-off-by: Andrew Janke <andrew@apjanke.net>

Long term it would be nice to sandbox everything that writes to DerivedData
but it is essentially a cache directory of sorts.

The downside of allowing stuff to write there particularly is that DerivedData
is notoriously bad at getting cleaned up, so if you do a lot of Xcode-using
installations very quickly, you can chew your disk space up.

Closes Homebrew/homebrew#43276.

Signed-off-by: Dominyk Tiller <dominyktiller@gmail.com>

These are minor perf optimizations.

Closes Homebrew/homebrew#43028.

Signed-off-by: Baptiste Fontaine <batifon@yahoo.fr>

Closes Homebrew/homebrew#42593.

Signed-off-by: Xu Cheng <xucheng@me.com>

Closes Homebrew/homebrew#42293.

Signed-off-by: Xu Cheng <xucheng@me.com>

Closes Homebrew/homebrew#38792.

Signed-off-by: Xu Cheng <xucheng@me.com>

Closes Homebrew/homebrew#38711.

Signed-off-by: Xu Cheng <xucheng@me.com>

Closes Homebrew/homebrew#38479.

Signed-off-by: Xu Cheng <xucheng@me.com>