ruby version of SetEquate script

Ghidra comes with a number of scripts included which serve as both examples of the sorts of things that can be done with scripts as well as perform some useful tasks. Ruby Dragon includes examples itself to show how things written in Java/Python can be done in the languages that it adds to Ghidra. More of these example scripts will provide a greater base of examples for users to refer to when writing a script in their language of choice.

Implement a Ruby version of the [SetEquateScript](https://github.com/NationalSecurityAgency/ghidra/blob/master/Ghidra/Features/Base/ghidra_scripts/SetEquateScript.java) included with Ghidra. This should go in the `ghidra_scripts` folder, along with the other examples, and be put in the category `Examples.Ruby`. The existing Ruby scripts will give you some examples of the basics of JRuby and using it within Ghidra.

Of course, please ask any questions you have here if you get stuck!