Sized binary search tree

• Nievergelt & Reingold <1+sqrt 2,sqrt2> (METHOD=1)
• Roura (METHOD=2)
• Adams (4,2) (METHOD=3) -- this is the default code
• Adams (3,2) (METHOD=4)
• Nievergelt & Reingold <3,2> (METHOD=5)

Tests with HUnit and QuickCheck

You can run tests:

% cd test
% runghc -i.. -DMETHOD=1 Test.hs
% runghc -i.. Test.hs --maximum-generated-tests=10000 -t difference