stac.corenlp: also work with live data
Sort nodes by text span in enclosure graph
cdu-stripping corner case, handle loops
Remove educe.stac.csv

That sort of thing really belongs in STAC proper
csv module no longer in docs
Make dependency tree searchable
Rely on NLTK tree iterable instance for search

Do not require a children field
This field should probably go away
Export link element in dependency graphs
More efficient enclosure graph mechanism

Note that we now just build pre-reduced graph.
Before, algorithm was just to build up potentially O(n^2) links
and then chop them back down with reduce.

Now, we group the annotations by size and build up, only
connecting to the largest nodes we can enclose
Hopefully allow pydot externals