Added graph coloring algorithm inside Greedy

[ritikverma2000]

Graph coloring problem is to assign colors to certain elements of a graph subject to certain constraints. Vertex coloring is the most common graph coloring problem. The problem is, given m colors, find a way of coloring the vertices of a graph such that no two adjacent vertices are colored using the same color. Chromatic Number: The smallest number of colors needed to color a graph G is called its chromatic number. So basically my code finds the chromatic number for the given graph.

[ritikverma2000]

@ericklarac if you could pls check my code and merge it in your repo it would be great as it an urgent requirement for me.