Changelog for IntervalMap- Add IntervalSet. Minor performance tweaks. Documentation updates. Moved to GitHub. Documentation update. Wrong portability info fixed. Major update adding support for user-defined key intervals. Updated benchmark to use Criterion 1.0. Tested with ghc 7.8.3. Dropped upper constraint on criterion. Tested with ghc 7.6.3. Migrated repo to Darcs Hub. Bugfixes: Lazy was too strict, Strict too lazy. Split into Lazy and Strict modules, following containers.