Implement Min/Max view functions.
Implement updateMin, updateMax and equivalent withKey functions.
Rewrite deleteMin, deleteMax in terms of updateExtremity.
Add a test for null

Adapted and simplified from a pull request by Ramses de Norre.
Fix deleteFindMin
Fix deleteFindMax
Small improvements to the test code.
implement updateWithKey and rewrite delete to use this
remove old delete function and benchmarks
Merge pull request #20 from bcdarwin/master

implement updateWithKey and rewrite delete to use this
Merge