Add lex tokens to interactive import
Get rid of redundant constructors
Cleanup BDD module public interface

Added upoint2bddpoint and BDDNode,
removed bddnode and bdd.
There is really no reason for a user to use the bddnode/bdd functions to
directly construct BDDs.
Overhaul BDD traversal methods

Instead of just a traverse (dfs preorder), now we have:
* dfs preorder, inorder, postorder
* bfs
Bump BDD coverage to 100%