Rdoc Enhancements for Hash Completed

I've finished my enhancements (revisions, really) of the Rdoc for Hash. They will be seen in the next release, but may be seen now at:

• https://docs.ruby-lang.org/en/master/Hash.html.

My main goal was to have example code for just about everything.

The current Rdoc is at:

• https://ruby-doc.org/core-2.7.1/Hash.html.

I've begun work on Array.