Added post-order traversal to forest walker
Gideon : Refactored the Rule Interface and its implementing classes.
MonoLingualRule is removed, its contents merged with BilingualRule.
A new class RuleMethods is added to avoid code duplication in the implementation of the
Rule Interface's methods.
Some new Extra query methods for nonterminals etc are added, which are helpfull for computing
certain discriminative features with respect to the rule labels.
renamed TRAVERSAL
Massive cleaning, double -> float conversion, renaming for readability, and commenting. Also started on forest restoring.
Bugfix: set forest walker to default to preorder traversal
Bugfix: restored root symbol to fix test cases
Merge branch 'master' of https://github.com/gwenniger/joshua into gwenniger