Functor Coloring.Make

module Make: 
functor (G : G) -> sig .. end
Provide a function for k-coloring a graph.
G : G

module H: Hashtbl.S  with type key = G.V.t
Hash tables used to store the coloring
val coloring : Coloring.G.t -> int -> int H.t
coloring g k colors the graph g with k colors and returns the coloring as a hash table mapping nodes to their colors.