Swich to vendoring dependencies with `dep`

[ci skip]

Done by `dep init`

[ci skip]

Support for `commentchar=auto`, always respect `--edit`

This shows commented-out text such as "Creating an issue for github/hub"
not only when `-m` or `-F` weren't passed, but also when they were
passed and `--edit` was used.

The commit body comes first, then template text. This is for
compatibility with GitHub web interface.

Fixes #1657

Previously, passing `--edit` in combination with `-m` would skip opening
the editor. For compatibility with `git commit`, `--edit` is now always
respected.

Have CI fail if go code wasn't properly formatted

Fixes #1654

Add -p flag to pull-request command usage

Mention fish completion with bash and zsh

Have `fetch` use writable push URL for writeable fork

This is to avoid having a writeable fork added with `git://` protocol
(the default when `hub.protocol` is not configured).

This matches the behavior of `hub clone`.

Enable team reviewers in `pull-request`

Spelling

Fix recognition logic for vi editor variants again

Ensure that _git completion func is replaced only once.