Added mapEdges
Added mapEdges tests
Removed unnecessary edgeKeyType field
Updated the Graph constructor
Added mapEdges to the tested methods
Merge pull request #6 from balidani/master

mapEdges implemented
fromCollection(vertices, edges) implemented and tested
Merge pull request #13 from andralungu/fromCollection

fromCollection(vertices, edges) implemented and tested
added create methods from set of edges
Merge pull request #15 from vasia/working-only-create-methods

added create methods from set of edges
fromCollection(edges) implemented abd tested
Merge pull request #17 from andralungu/fromCollectionEdges

fromCollection(edges) implemented and tested
resolve merge conflicts