Add more Graph Algorithms

[master-fury]

This category has very less scripts, Add some new scripts. #33

[may55]

Hey, @master-fury I would like to add Prims, Dijkstra to the category.

[master-fury]

Hi, @may55 Please go-ahead.

[may55]

@master-fury Yes, I'll submit the PR on or after 1 Oct, for hacktoberfest.

[CaptainLazarus]

Graph algorithms for directed graphs (flow-sink problems) allowed too or only undirected graphs?