Implement Clone, Eq and Hash for the heap and stack

Implement Clone, Eq and Hash for the heap and stack

I use a pattern binding in each custom impl, so that adding fields to
`Memory` or `Frame` will cause a compiler error instead of causing e.g.
`PartialEq` to become invalid. This may be too cute.

This adds several requirements to `Machine::MemoryData`. These can be
removed if we don't want this associated type to be part of the equality
of `Memory`.