Renamed TypeRef to TypeGraphRef
Initial definition of type equation datatypes
Broke lots of things. Woo.
Functions now store parameter_ptr_dynarrays

Also made it so empty expressions default to 3 (for now). Why? Because
it'll make it easier to play with type inference for now.
Switched prims to use type_refs
Removed "known" attribute of TypeInfo

Functionality now handled by type_ref
Added initial generation of type equations
Added methods to print type equations
Initial definition of argument restrict rule
Made print_type_ref print letters

(this is a really dumb hack, used only for debugging purposes)
Parameter types now properly associate with cells
Added "for_every" to simplify rule implementation
Added "with_polymorph" to further simplify rules
Added stub of expand_apply_rule
Created equation_set to simplify things
Renamed "get _ eqn" to "get _ RH" (more correct)
Encapsulated replacement of equations
Made drastic changes to structure of typerefs

Now going to be using unification
Corrected "make_empty_type"s to "make_unknown_type"s
Changed type activity rule