rpn 8.5.0 is released: Big Clean-Up and Documentation Release!

Much more thorough argument validation has been implemented on all operators. In addition, all non-constant operator function names now end with 'Operator', which means I can be sure they are not being called recursively, or being called by other operator functions, so that the argument expansion and validation isn't being done more than once.

I have continued my focus on completing the online help, which is now more than 95% complete. This also resulted in a number of operators being eliminated (see below), and a bevy of bug fixes. Almost every operator now has a help example.

The help for units is now complete. Every unit has help text.

About 70 new operators have been added.