Flow methods should have standard arguments and return values

[kennethbruskiewicz]

The three flow functions (find_cflow, find_gflow, find_pflow) all have very different implementations. However, as they are all concerned with finding flow, I believe they should share parameters and outputs as much as possible to hide the differences and complexity of each function.

find_glow returns two lambdas and a max value as a part of its return type? I don't know what's going on there but it makes it more difficult to test using assertions when the return values vary in this way.