Generic coalesce functions

Some of the algorithms in this module do complex recursive operations on sequences of patches in order to simplify them. These algorithms require that we know whether some intermediate step has made any progress. If not, we want to terminate or try something different.

We capture this as an effect by tagging intermediate data with the Any monoid, a newtype wrapper for Bool with disjunction as mappend. The standard instance Monoid a => Monad (a,)' defined in the base package then gives use the desired semantics. That is, when we sequence operations using >>=, the result tells us whether Any of the two operations have made progress.