Add Implementation for Prim's algorithm

[jafar75]

Hi there, It is known that Kruskal's algorithm for finding MST, has a simpler implmentation than Prim's and also is more efficient for sparse graph. If it is needed, I'm willing to implement prim's algorithm, as it is more suitable when the graph is dense. useful link

[samueltardieu]

Hi @jafar75. If you have any use for it, please do, I'd be happy to integrate it.