Apple changed the name of their operating system from OS X to macOS a number of years ago. This was overdue!

As per issue  #10311

* refactor(osx): rename `osx` plugin to `macos`
* refactor(macos): Add symbolic link from old `osx` plugin name.

Co-authored-by: Marc Cornellà <hello@mcornella.com>

Fixes #8212

Co-authored-by: Sean Hellum <seanhellum45@gmail.com>

The ZSH_THEME_RANDOM_BLACKLIST variable will be deprecated until it's
removed 2 months from now.

Note: `upgrade_oh_my_zsh` is deprecated. Use `omz update` instead.

Co-authored-by: Marc Cornellà <marc.cornella@live.com>

Co-authored-by: Marc Cornellà <marc.cornella@live.com>
Co-authored-by: Bartek Pacia <barpac02@gmail.com>

The published workflow tests the installer and checks the syntax of known zsh files
in the project.

Co-authored-by: Marc Cornellà <marc.cornella@live.com>

Moving down below the intro copy so that first content to new-comers is a description of the project

* Change project URL from robbyrussell to ohmyzsh org

* Update git remote to use ohmyzsh org repository

Co-authored-by: Emil Engler <me@emilengler.com>
Closes #8157

The original suggestion for an unattended install downloads the installation script to a file, then runs that file with the --unattended argument. The install.sh file would be left behind after the suggested command was run.
This change passes the --unattended argument directly into sh. So, it's a nice one-liner like the default installation script, and it doesn't leave a dangling install.sh script.

After wandering into a few articles that discuss the difference between might and may...opting for may.

Add important notice about `chsh -s /bin/zsh` command requiring the user to log out and log back in to see the changes.

Introducing a Code of Conduct based on the Contributor Covenant project. Adding links from the README and CONTRIBUTING pages to this, too, along with an email address for reporting abusive behavior to. Closes #7733 (#7734)

* Updating Oh My Zsh shop URLs

Linking directly to the Oh My Zsh inventory vs the top-level store with non-OMZ items.

* Updating link to Oh My Zsh products in the install script

* Updating link to Oh My Zsh shop products in the upgrade script

* Getting rid of 't-' in shirts for now

The git:// transport is completely unauthenticated. An attacker on the local or upstream network can easily man-in-the-middle an oh-my-zsh update and get remote code execution on your system. Only the https:// git transport should be used.

Updating template and README to list plugins on individual lines vs one long one. Easier scanning for you and me.

* README.md: shit load -> shit-load

* README.md: shit-load -> shitload