Fix tmux_pane_content test helper

Fetch all releases when doing `hub release`

Fixes #1511

Fix PATH update in windows installation script

Fixes #1506.

Ignore all lines that are printed before the first command prompt. On
some systems bash prints a message about how to use the sudo command
when started with a clean `HOME`, causing some tests to fail.

Fixes #1477

As suggested at #1511, instead of fetching only the first 30 releases,
follow the `next` link to fetch all pages.

Document available environment variables

travis: update go versions

As discussed at https://github.com/github/hub/pull/1573

Enforce unix eol in bash script files through .gitattributes

Contributor Covenant Code of Conduct

Document the availability of the development version.

Pass file descriptors to cmd.NewWithArray

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