and a couple of the other related functions:
- addRTFunction is now an overload of FunctionMetadata::addVersion
- boxFunctionMetadata is now createFunctionFromMetadata (it doesn't return a box)
- createRTFunction was just a wrapper around new FunctionMetadata(), so get rid of it
- boxRTFunction is now FunctionMetadata::create

"CLFunction" never really made sense as a name, and some of the other related functions
didn't make sense either (especially after a couple refactorings happened).  Hopefully
this makes it less confusing.