sparsify

Graph sparsification

Functions

`conductance_weighted_graph`
`edge_sampling_sparsify`
`effective_resistances`	compute effective resistances
`hierarchical_sparsify`
`nearest_neighbor_sparsify`
`relaxed_spanning_tree`	compute relaxed minimum or maximum spanning tree
`resistance_sparsify`	Sparsify a graph to have a target mean degree using effective resistance based sampling
`resistance_weighted_graph`	modify the edge weights of a graph by multiplying by their effective resistance