Began work: builds the tree and normalizes
Tree builder: remember parents
Large framework update:

- Apply_rule_set applies a named rule set for a named locale.
- node.iterate(): bredth-first iteration over all nodes.
- NoSuchRuleSetException: raised if the named ruleset doesn't exit.
- Renamed tree to math_tree.
- global function to execute a rule set on an xml fragment.
Huge amount of fixes and a test script