Merge pull request #18 from arne-cl/master

fixed README. PyPI package name is disco-dop, Cython needs to be install...
inside/outside probabilities for PLCFRS charts

- inside/outside probabilities can now be computed for both PCFG and PLCFRS
	charts, makes pruning with posterior thresholds possible.
- with RR-parsing, leave out adjunctive functions from the horizontal
  context of markovized binarization.
Add XPath queries to treesearch

When the alpinocorpus-python module is installed, and corpus files are
available in .dact format, the original discontinuous trees can now be
searched using XPath queries.
compile-time condition to ensure FatChartItems can hold 128 bits.
replaced calls to xml.etree.cElementTree with lxml.etree to get rid of UTF8
problems (issue #19).