are stored in the tree are simply pointers, which
are assumed to contain the keys and data.
<p>
The caller supplies a comparison function, for example
<pre>
    Ordertype compare(void *v1, void *v2)
or
    Ordertype compare(struct my_data *p1, struct my_data *p2)
</pre>
that is assumed to return LESS_THAN, GREATER_THAN, or SAME_AS.
<p>
Aside from the ordinary "insert", "find", and "delete" operations,
there is a "position" operation that tells where an item is
in w.r.t. the inorder traversal of the tree, an