Update corenlp to version 3.4, XML output

CoreNLP 3.4 allows XML output in interactive mode,
so we use that instead of parsing the plain text output.
The existing corenlp_xml module does most of the hard work.
Fix xml interpretation for multiple sentences
Merge pull request #63 from vanatteveldt/corenlp_3.4_xml

Update corenlp to version 3.4, XML output
upgrade to scikit-learn 0.15.1
micro-optimize: use cytoolz instead of toolz
release 3.0.1
fix Debian installation instructions

* packaged six is too old (even on Debian 7)
* LXML is too old (for corenlp), build needs libxslt
* no NLTK package, like in Ubuntu
* Frog dependencies
improve task docs
Merge branch 'master' into py3

Conflicts:
	.travis.yml
Py3 reqs: new NLTK, scikit-learn; toolz -> cytoolz