GitLab

- Removing head of list of observations after each reduction step in definition of wp
- Adding support for observations to state_interp and world
- Applying Ralf's suggestions to previous commit (e.g. replacing /\ and -> with unicode characters)

* move PROP-envs definitions to environments.v so that we can control them without pulling in coq_tactics
* use reduction-controlled `pm_default` for proofmode accessors

The BI interface is then instantiated using these laws.  In particular, this
shows that the rules we claim to be admissible actually are.

Fixes #193

New atomic updates: defined as a fixed point with existential quantifier; intro lemma using class of Laterable assertions

move test suite out of theories/ so it does not get installed; also check output of test suite so that we can test printing

Based on an earlier MR by @jung.