created the priority queue heap thing with tests
fixed extra line issue
restructured tests
refactored code
Merge pull request #6 from jefrailey/heap

Heap
added peek method and corresponding test
Add test_simple_graph.py and simple_graph.py with test_nodes_empty() to assert that a graph is initialized without nodes
Update test_nodes_empty() to account for AttributeError; update simple_graph with Graph()
Revise Graph() to initialize with emtpy lists to contain nodes and edges instead of setting them to None
Update tests to account for the new initalization of Graphs
Revise Graph() to hold edges and nodes in a list since we decided that edges and nodes will be instances of class objects
Revies tests to account for new Graph() structure
Add tests for initalizing nodes, adding nodes to a graph, and adding edges to a graph
Add Node and Edge classes
Add Graph.add_node() to instantiate nodes and add them to the graph
Revise (yet again) the internal representation of nodes and edges--they're strings/tuples in a set
Update tests based on changes to simple_graph.py
Add tests for .del_node() and .del_edge()
Add del_node() and del_edge() to Graph()
Add test_has_node() to test if a node exists in the graph