GitLab

- Better representation of symbolic integers
- Better representation of symbolic locations
- Support while in the vcg
- Support alloc in the vcg
- A better reification mechanism
- Better proofmode support for mapsto with lists
- Normalize fractions
- Restructure lots of proofs
- ...

(Fixes #4)

- Add support for fst/snd/pair to the vcg_gen + reified expressions for non-monadic expressions.
- Make `cloc_to_val` locked so that it will _never_ be unfolded.
- Support locations + offsets in the reified language.
- Drop `vcg_compute`, it left huge thunks of computation, making some things super slow. Just use `simpl` with appropriate `Arguments` instead.