Propagate global git arguments to Before/After chains

This fixes `hub -C mydir merge <URL>` and other commands that might be
invoked with git global arguments by ensuring that those global
arguments are also fowarded to any accompanying `git` commands within
`Before()` and `After()` chains.

Fixes #2107

Fixes #2102

This works around a GitHub API issue where it blocks PRs based on their
draft status even if they were `draft: false`.

Fixes #2099

Open draft pull requests with `-d` / `--draft`

Implement draft by adding a -d / --draft argument. Add setting header on
the API client for the moment as the feature is still in preview on the API

Fix compatibility with git when run with no arguments

Fix issue/PR labels output in no-color mode

Fixes this error:

    $ hub --git-dir=.git
    git: '' is not a git command. See 'git --help'.

Instead, help text is shown just like with normal git.

Right now this doesn't push to fork, but ideally it should if the person
doesn't have the permissions to push to upstream.

Allow repository names that start with a dash character

These are allowed on GitHub.

Linuxbrew is available on linux and WSL

[ci skip]

Fixes #2054 [ci skip]

Fixes #2066

Make `checkout` work independently of remote refspec

This fixes:

    fatal: Cannot setup tracking information; starting point 'BRANCH' is not a branch.

if the remote refspec is set up to only fetch specific branches and NOT
like the default `+refs/heads/*:refs/remotes/origin/*`.

I don't understand why would git, after fetching into
`refs/remotes/origin/BRANCH`, complain that `origin/BRANCH` is not a
branch, but there we have it. Setting up upstream tracking manually
works around this problem.

Add pull-request --no-edit flag to zsh completion

Documentation of install on Debian (sid/buster)

Squash on merge

Ref. #2043

Fixes #718 by documenting that the package is in the official repository now, or perhaps there is also a need for a package for the current stable Debian version.

List PR "Draft" state using the `--format` string

- `%pS`: "open", "draft", "merged", or "closed"
- `%pC`: green, gray, purple, or red

Have commands with rich output respect the `--color` flag

Add FreeBSD installation instructions

Make man pages parseable with `whatis`