RFC: Graph validators

[fushar]

We'll first provide an API to "build" a graph, to which we can then call the validators.

Ideas of graph builder methods:

• graphOfNodes(N).edges(U, V)

Need to find a way to specify whether the nodes are numbered 0-based or 1-based. Maybe something like

• graphOfOneBasedNodes(N).edges(U, V)
• graphOfZeroBasedNodes(N).edges(U, V)

Ideas of graph validators:

• .isForest()
• .isTree()
• .hasNoSelfLoops()
• .hasNoMultipleEdges()