Added Monoid instances to Summaries.
Added NFData instances.
Upped the version constraints on vector, and added a deepseq dependency.
Fixed the monoid instance. It was just plain broken before.
Corrected the definition of 'delta'.
Fixed the case where n == 0.
CSE, because GHC won't do it for me.
Added monoid instance tests.
Added monoid associativity tests.
Refactor Summary union code
Simplify NFData instances
Rename summary assoc test to commute test; add proper summary assoc test
Bump version number; update NEWS