CachingEvaluation: drop design prototypes

It's interesting to read the comments and see how hard it was to come up
with the correct semantics --- we should mention this in the paper (on
it). This drops 3 (incomplete) versions of the semantics.
Clarify comment
Rename
Reorder code

Separate non-CBPV and CBPV version of the code
Drop non-CBPV caching semantics & update comments