Group corpus & binarization parameters; closes #27

- runexp: group some options under traincorpus, testcorpus &
  binarization; use DictObj for them.
- runexp: verbosity levels given as integer
- runexp: additional verbosity level to dump derivations & parse trees
- runexp: rename 'dop1' estimator to 'rfe', since that is a more specific
  designation.
- disambiguation: split marginalize() into function for getting
  derivations and doing actual marginalization.
- disambiguation: use chart.grammar instead of superfluous grammar argument.
- treebank: treebanks are specified with a single path, instead of combination of
  directory and filename.