faster-train

This is an implementation of "A Discriminative Reordering Parser for IWSLT2013"

* Apply Cube Growing with cell-level CYK parallelization
* Generate features in parallel
* Save the generated features on disk

Because I had been working on the forked branch far ago (9c13ba8fefacd30160547656f51e7f6a04e031ee), I merged the improvement into the latest larder/master (8a2cb4dbcb073ed2142a14964dca0e134455f51f).

At this moment, Cube Growing does not seem to speed up the training. I'll further investigate the difference between my implementation and the merged one.

Parallelism and storing features on disk work fine. Feel free to use them for faster training!