Ran the 2to3 script on nltk_contrib/

[alex-calderwood]

After running the script to convert the package to python 3, I manually fixed runtime errors in the nltk_contrib/fuf/ module. So far that is the only module that I've tested, but before merging this into master, the rest of the modules should be tested as well.

I think this should be merged into a new branch (say 'python 3') so that others have easier access to a rough python 3 implementation of nltk_contrib. It will take some time to test all of the modules.

[tomaarsen]

@stevenbird Are you willing to accept this going straight to master? I've set up a python3 branch if you want to push it there first.