Closes #517 [ci skip]

[ci skip]

Fixes #421

This feature is likely to get dropped from GitHub API in the near
future. The alternative is to simply create a new pull-request and
reference the original issue in the description.

[ci skip]

Signed-off-by: NTimothy Gu <timothygu99@gmail.com>

Don't suggest standalone install via curl anymore because:

- hub may not be a single script in the near future
- `rake install` handles the Windows executable as well

Emulates the interface of `git commit`:

  $ hub pull-request -m "This is my title"
  $ hub pull-request -F /path/to/message.txt
  $ hub pull-request -F -

The old way of passing in just title is deprecated

  $ hub pull-request "Deprecated title"

Fixes #183

Fixes #232, references #270

Fixes #254

It doesn't add a remote anymore, as it isn't needed.

Now forwards flags to internal `checkout` command, resets the existing
local branch by default.

Closes #132

Closes #118, references #111

Closes #75

Closes #93, references #65, references #49

Closes #91

GitHub doesn't support ranges with two dots, only three. With these two
being equivalent in case of linear history, it's generally safe to convert
the range pasted on the command-line to three dots. This is to avoid
confusion where GitHub would display a 404 page otherwise.

See "specifying ranges" in the `git-rev-parse` man page.

closes #80