Cleaned node removal method and fixed consistency bug.
Python has no semi-decent built-in priority queue. wat.
Updated SXT algorithm to use a priority queue.
Added further test coverage.
Removed old undirected hypergraph class; [very] obsolete.
Removed old base hypergraph class.
Moved priority queue class; updated references appropriately.
Merge branch 'master' into yaserkl
Modified node and hyperedge ID iterators + added corresponding tests; made pep8 compliant.