Created add_node function to accept node by name or by Node object
Added test for add_node
pep8 compatable
Added code to inforce Node name must be unique.
Added tests for uniquesness
Merge branch 'UniqueNodeName'
Changed addNode methods to underscores, made names imply private and updated self._node references
Added test for invalid Node instance in add
Added test for invalid Node instance in add
Merge branch 'mohammed' of https://github.com/tmmurali/hypergraph into mohammed

Conflicts:
	tests/test_add_node.py
Fixed bug in get_node_names
Added test for get_node_names and get_nodes_by_name
Merge pull request #13 from tmmurali/mohammed

Mohammed
Added tests for node.py
Merge pull request #16 from tmmurali/mohammed

Added tests for node.py
Merge remote-tracking branch 'origin/master' into matt-mohammed