Error when user forgets to use `pearlite!`

[xldenis]

We should detect and provide a helpful error when the user forgets to use pearlite! { .. } in predicates or logical functions.

see #378

[jhjourdan]

Or make it implicit in logic and predicate functions?

[xldenis]

We can't since attribute macros need to be attached to valid rust syntax, so there's no way for us to handle ^, forall, exists or other logical operators.

[xldenis]

We now provide an error message when logical symbols are used outside of pearlite! contexts.