* 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

Closes #5681

Closes #5558

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

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

From `raw.github.com' to `raw.githubusercontent.com'

Fixes #4933

Also, fix a couple of typos / style issues.

 - Adding documentation
 - Note the effect empty array
 - Fix spelling
 - Using new test `[[...]]`

The tilde character is not expanded when inside quotes. See https://github.com/robbyrussell/oh-my-zsh/issues/4668#issuecomment-162213379

Change http://ohmyz.sh link to use proper markdown syntax

Fix typo

A few spelling fixes, grammatical fixes (what's with all the ellipses?), some standardization of capitalization, and a few other tweaks.

As well, I changed all standalone code fragments into proper code blocks.

I also added a missing theme image!

Updating the install instructions as proposed in: https://github.com/robbyrussell/oh-my-zsh/issues/3516#issuecomment-76506726

Resolves #3786