In case when the PR's head and base repositories are the same, check out
the new branch in a way that sets up push workflow to the same branch.

    git fetch origin +refs/heads/fixes:refs/remotes/origin/fixes
    git checkout -b fixes --track origin/fixes

The remote needs to match the base project from the pull request.

Instead, specify timezone offsets explicitly so that different
environments interpret the time identically.

Renamed some existing placeholders and added new ones such as milestone
number/title, raw labels, comma-separated assignees, and number of comments.

Fixes #1227

This allows accumulating values across repeated arguments.

Now `hub remote` will only prompt to select from your configured hosts
if it can't infer the GitHub hostname from existing remotes.

In case you're prompted, and you choose a GHE host, now that choice will
be properly reflected in the generated URL, unlike before when it would
always revert to "github.com" regardless of choice.

Fixes #1141

When the repo that hosts the `head` for the PR is moved to another
owner, the `owner:branch` specification will be wrong and the GitHub API
will return HTTP 422.

This resolves the latest owner/name pair for head repo so that the value
is never stale when submitting new PR to be created.

Fixes #467

Also, adopt the new name of the fork more precisely so it's reflected in
the new remote URL. The name of the new git remote is for now *not*
inherited from the returned Repository object for backwards compatibility.

Fixes #1178

This ensures that the final repository URL cloned will have the
repository's actual name after redirect.

Implements the GeneratePRTemplate in pull_request.go instead of the
custom logic that previously existed in the file.  Addresses:

* Title being defaulted as the first line of the template
* Commit messages not defaulting as the title only properly

The description for --head said it was the head branch instead of head branch.

Remove (beta) from help.go for release and issue.