#88 Enhance typing system to deal with heterogeneous lists

[Bruce Merry]

The current .bc files cannot describe a pointer to a list of elements of different semantic types. Currently this is handled by overriding the dumping function to customize the display of the elements, and even then it has limited success. A fully general replacement would allow a function to accept a marshalled call object and produce a tree of information. Each leaf in the tree could include raw value, semantic type and dumped string value.