Committing temporary modifications made to help solve the bug where the DIET gets unbalanced and corrupts the set of values it holds.
Specialized the Diet type for the 'char' type and renamed it to CharDiet. Removed (for now) the Range struct so we can use the tuples as in the original CamlDiets code; this is slower but easier to work with.
Removed the explicit comparer argument from some functions in the AvlTree module -- now we use the comparison method provided by the type (which must support the 'comparison' constraint).
Removed DIET testing code.