Removed dead dijkstra code, fixes #13
Removed mutable from concrete names
Attempt at better NewNode
Deleted a leading space in comments
Removed useless convenience constants
Up and removed VetMutableGraph
Fixed mutability assertion
Removed EmptyGraph
EdgeBetween->UndirectedEdge (same for EdgeTo->DirectedEdge)
Directed->Undirected in MutableGraph (oops)
Refactoring
Refactoring
Added util.go (was added earlier but forgot to add it to source control)
Removed existence checks from AddNode (interface says new calls overwrite old ones)
Updated documentation to make Add...Edge requirements clearer on nodes
Merge branch 'mutable-changes' of github.com:gonum/graph into mutable-changes