This (horrid) hack reads cdec's "--show_derivations" and "--extract_rules" into
data structures  and tries to align "groups" in source and target sides
of rules in a smart, presentable way. The result resembles a phrase-based
system, given that the word alignment gives enough hints.

To run:
    ./derivation_to_json.rb < {one of the .raw files}
(first line of stdout is json data, source and target strings follow after that)