Refactor some methods to ease their usage.

    * ADD tests to slist
    * REFACTOR "*_ITERATE" methods
More fixes and minor modification

    * ADD hash table tests
    * REFACTOR entire hash table interface
Change manner in which splaytree operates (make it more like scapegoats)

    * Add success parameter to insert operations on btree's, as if a key exists, insert will fail.
Fix btree_find and htable_find

    * FIX a nasty bug in btree_find prevented the root from being compared correctly.
Add missing testers and headers