predicates now take a basis-t value as a first argument as well as the value (set of values) at that basis-t

this allows for nesting temporal operators, as the basis-t is passed into sub expressions
remove special case for eventually-globally

- this can be now be expressed as a proper nesting of eventually and globally
- turn the original definition into a test
add in an alternate expression of weak until that requires nesting

- ɸ W ψ ≡ ɸ U (ψ ∨ (G ɸ))
- add equivalence as a marginalia doc
- add as a test
correct doc string for ltl/release