Now using strings of words instead of strings of IDs
Added -rescore-forest option, removed -oracle-file

If you want to pass in an oracle / reference sentence, it is the third |||-delimited
field on STDIN to Joshua. Probably some effort should go into rethinking the STDIN
input format; currently the second field is used for a target-language parsing or
forced-decoding target, which is why we used the third field here.
Removed rescore() function and unused imports
Completed Stats class and BLEU scoring of Rule objects
Extended to handle references from the command-line.
Refactored Rule interface and replaced ArrayList<Integer> objects with int[]s
Added BLEU restoring of DerivationState objects, simplified interface a little bit
Updated test cases (changes caused by rounding errors)