ACES should support "or" constraints over windows, not just "and" constraints.

[mmcdermott]

E.g., in a window, the patient should have either an instance of taking medication A or medication B (which could occur at separate times.

This could likely be solved in a hacky manner via #43, but dedicated support would be preferred.

[mmcdermott]

This actually should have lower priority for now because you can use the predicate language to handle this -- though there are likely situations where that won't work. E.g., have a predicate of med_A_or_B then impose a constraint on that predicate, rather than a constraint on the individual med_A and med_B predicates over the window.

[mmcdermott]

This may overlap with #54