Fix corenlp results parser (NLTK API change)

It looks like we used to rely on NLTK 2's ability to pass
a tree string to the __init__ function, but that this is now
a fromstring class method.
Expose functions used by STAC dialogue_acts script
FIX: regression in Orange csv output

The tab format uses 'd' for discrete, but the CSV one uses 'D'
Long term, we should just switch to the tabbed format everywhere,
but this may involve tweaking some of our infrastructure
More robust graphviz output.

Unfortunately pydot does not seem to quote graph names,
so we have to munge them to avoid confusing graphviz.
ENH unfinished functional tag stripper
ENH delete empty nodes, strip function tags
ENH force rst_dt.ptb to output clean trees
stac-learning weave: tweak attelo output

Mostly inject EDU text, but also strip group id and convert
offsets to int (attelo lets them be float in case you want to
give it something like timestamps, etc)
MAINT minor code improvements after kowey review
Merge branch 'master' into ctree-remove-functional-tags
educe.stac.util.annotate.schema_text()

Display schema type annotations in a friendlier way,
cutting out intermediary context

  [m1]...[[m2.1]...[m2.2]..]...[m3]

But note that this isn't particularly clever, and if one
of the members includes another (which can but should not
happen), the text will be off.
Use schema_text in sanity checker output
Use schema_text in glozz dump
ENH is_empty_category
MAINT pep8 and pylint
FIX filter empty tokens after dirty tweaking
stac-learning weave: output dialogue acts too
FIX crash for basket features with missing PTB data
Merge pull request #15 from moreymat/fix-basket-no-ptb

FIX basket feature extraction with missing PTB data
FIX unigram feat ptb_pos_tag_last