add runtime folding, a few axioms used in the Agda experiments
SO close to making fields work...
Fixed fieldOf, still need fieldUpdate fixed
totally rework fields, move to typeclasses per field rather than fin and Coq's pattern matching.
Not sure how well the typeclass resolution will work with cleaner syntax.
Fields actually working with a general tie b/t field reads and getf
Put PLDI talk example in the right branch
Merge branch 'dev'

Conflicts:
	AppendOnlyLinkedList.v