added a new class for undirected hypergraph algorithm. Changed all the undirected graph methods based on the sparse matrix
Merge branch 'master' into yaserkl
Modified node and hyperedge ID iterators + added corresponding tests; made pep8 compliant.
Removing TravisCI testing until scipy issue is resolved.
Moved undirected_algorithm into algorithms folder; updated references accordingly.
Moved undirected_algorithm test into proper folder
Merge branch 'master' into yaserkl