Name CFunctions

[simonbates]

When I am further with my serialization and implementation of image-based storage [#7], I will need some way to name CFunctions.

Right now, if I implement table printing, I would get something like this for a signal:

{ step <CFunction> }

But which CFunction?

Sketch of an initial idea:

1. a hash table storing mapping from string name to function pointer
2. functions must be registered in this hash table
3. the CFunction object includes the name in addition to the function pointer
4. SetGlobalCFunction takes a name (which is looked up in table 1) rather than a function pointer directly
5. when we print a CFunction we get <CFunction:NAME> or such
6. when we read <CFunction:NAME>, we look up the table 1

MakeCFunction would also take a name rather than a function pointer.