Adding verbose keyword and functionality to sinkhorn

[Remrem08007]

Could it be possible to add verbose option that allows us to get feedback on the infinity‐norm of the marginal violations at each check, so you can see if it’s creeping down or at least if it has converged or not.

[devmotion]

Such convergence information is printed if you enable debug logging, e.g. by setting ENV["JULIA_DEBUG"] = "OptimalTransport" in the REPL or - more fine-grained - by using a logger with debug logging enabled when performing the Sinkhorn algorithm (see https://docs.julialang.org/en/v1/stdlib/Logging/#Example:-Enable-debug-level-messages for an example of how to do that).