Fix windows build

Add plan9port rc shell support

Add Fedora Linux installation instructions

Add ability to delete releases

Fixes https://github.com/github/hub/issues/1423

When any of these global flags are passed, don't try to decorate the
output as if `git help` was invoked.

Fixes https://github.com/github/hub/issues/1446

`git rev-parse --show-toplevel` returns an empty string with success
status when inside a bare git repo.

This avoids the go crash and also tweaks `hub issue` and `hub
pull-request` to work even if current working directory name couldn't be
obtained because it's only used for looking up issue/PR templates, which
isn't critical functionality.

Fixes https://github.com/github/hub/issues/1331

Remove trailing slashes from the $TMPDIR variable

Fix Code of Conduct hyperlink in CONTRIBUTING

Sort hub commands

reset-console

The rest of the sections are sorted alphabetically. This makes the hub
commands easier to read by sorting them the same way.

The expected HTTP status code is 201

Fixes #1463

Upgrade to Go 1.8

These were both requested during code review.

1. Removed the check_go_version script
2. Only check go version in bootstrap
3. Simplify the go version check logic

Fix bash completion test on MacOS X

The previous commit created the requirement that hub be built and
tested with no earlier a version of go than 1.8.

The only thing that has substansively changed is that Go 1.8 handles
redirect logic more safely than previous versions. This means we can
drop our special handling to avoid following redirects to other
domains. We were only doing that to protect against the possibility
of leaking auth headers. With Go 1.8, the auth headers are not
forwarded when following a redirect to another domain, so we don't
need our special handling any more.

As long as people are attempting to build with the Makefile, the new
check_go_version script should cause the build to stop if our
collaborators aren't using at least version 1.8 of go.

Allow the unsorted expansion for the fish shell

The useless assignment was causing the cucumber test suite to fail
even when the completion scenarios were skipped.

However my git installation was run, it installed the
git-completion.{bash,zsh} scripts under
"${GIT_PREFIX}/contrib/completion/" instead of any of the paths that
this test case was expecting.

To make matters worse, the only way to know that this was the problem
was that each scenaro failed with a message about timing out while
waiting for completion to happen in tmux. Just in case there are
other paths out there where the git-distributed completion scripts
may live, I've also added some detection logic to raise an exception
during the "Given" clause of the scenario if we cannot find the
git-distributed bash completion scripts in any of the places we're
looking for them. This would have made it a lot easier to diagonse
the failures.

Before this change, the `pu` would sometimes expand to `pull
pull-request push` if the order isn't important, we should take this
fix.

However, if the order is important, we should probably switch the
expectation such that the options are presented alphabetically as
observed.

This is helpful for when TMPDIR already has a trailing slash. We can't
be sure that it will on all operating systems, but this will remove it
if it is there.

Add support for review requests in pull-request command

The GitHub API currently doesn't recognize multiple values of `Accept`
header, so ensure that `black-cat-preview` is the main one when
requesting reviewers.