Returns the flow hierarchy of a directed network.
Flow hierarchy is defined as the fraction of edges not participating in cycles in a directed graph [R184].
Parameters :  G : DiGraph or MultiDiGraph
weight : key,optional (default=None)


Returns :  h : float

Notes
The algorithm described in [R184] computes the flow hierarchy through exponentiation of the adjacency matrix. This function implements an alternative approach that finds strongly connected components. An edge is in a cycle if and only if it is in a strongly connected component, which can be found in time using Tarjan’s algorithm.
References
[R184]  (1, 2, 3) Luo, J.; Magee, C.L. (2011), Detecting evolving patterns of selforganizing networks by flow hierarchy measurement, Complexity, Volume 16 Issue 6 5361. DOI: 10.1002/cplx.20368 http://web.mit.edu/~cmagee/www/documents/28DetectingEvolvingPatterns_FlowHierarchy.pdf 