Closes #5681

* Add plugin for Swift Package Manager
* swift-package-manager: Rename plugin to 'swift-pm'

* yarn completion

Sourcing oh-my-zsh happens in zshrc, which will override settings of
profile and zshenv.  Treat misc values, `PAGER` and `LESS`, as default
settings without overriding existing values.

Fixes: #1, robbyrussell/oh-my-zsh#3016

Fixes #5623.

Closes #4988

`gls` seems to be installed by default or on most macOS systems, but its
default color scheme sucks. This fix will make sure to only use it if it
has been customised prior to running OMZ.

Related: #5516, #5520.

Closes #5594

PHP can be executed as CLI script but due to the automated attempt
to add browser support to that extension such ability is prevented
in certain circumstances.

Closes #5558

* add docker-compose down alias

* rename `docker-compose down` alias to `dcdn`

* Add a tip to ease agnoster first setup

* Change link to agnoster wiki + format changes

https://github.com/robbyrussell/oh-my-zsh/wiki/Themes#agnoster

https://github.com/robbyrussell/oh-my-zsh/wiki/Themes#agnoster

Closes #5568

Source:
https://github.com/docker/docker/commit/c9fdf9abf8d6443598808809b900d96e04adfcb1

* Add '#' instead of '$' when in root
* Make return code bold

Display suvash prompt w/o Ruby; refactor code

Change OS X to macOS in the README file in line with apples rebranding
of the operating system.

Change OS X to macOS in the read me file in line with apples rebranding
of the operating system.

Fixes #5520.