Ruby type equivalents

[daveworth]

I simply extended the type-equivalents table to include Ruby. Let me know if there are any changes you'd like to see.

[mdboom]

Thanks so much for the contribution. I was hoping someone would come along and do this.

There are other places where this information has been duplicated, most notably in reference/type.rst, but also when each type is documented individually. If you grep on .. language_specific:: you should find them. If you're able to take that on to make this "Ruby complete", that would be great, but if not, we can just merge this and I'll try to fan it out to the other locations, bearing in mind I don't know much Ruby.

[benjagm]

The changes are already in production.