Added ASCII visualization of trees, modified from the disco-dop project by Andreas van Cranenburgh
Renamed `Tree` method `visualize` to `pretty_print`
Renamed the class `TreeVisualizer` to `TreePrettyPrinter`.
Renamed the file `treevisualizer.py` to `treeprettyprinter`.
Merge pull request #794 from heatherleaf/treedraw

ASCII visualization of trees
Fix bug :  Stanford tokenizer -- request to add -outputFormat inlineXML #735
removed set and dict comprehensions for python 2.6 compatibility; removed u string prefixes for python 3 compatibility