Add Raiyan's edge weighted algorithm work

[mtorpey]

Raiyan did a bunch of good work on edge-weighted algorithms, which was made into PR #584.

My latest version of this work is at https://github.com/mtorpey/Digraphs/tree/edge-weight-algorithms from which I'm making PRs one bit at a time.

Approximate todo list:

• [x] EdgeWeightedDigraphMinimumSpanningTree: #650
• [x] DigraphEdgeWeightedShortestPath[s]: #656
• [x] DigraphMaximumFlow/DigraphMinimumCuts: #751
• [x] RandomUniqueEdgeWeightedDigraph: #755
• [x] Random strongly connected digraph (semi-related): #871
• [ ] DotColoredEdgeWeightedDigraph