This fixes issue #627

This fixes issue #431

This fixes issue #444.

This essentially replaces "neighbours" by "neighbors" throughout.

Aliases using the British spelling (e.g. Vertex.out_neighbours()) are
preserved for compatibility.

This returns an optional list of locations of the motifs found in the
main graph.

This also improves some of the existing shuffling strategies with a fast
alias sampling. The parameter names of the random_graph() and
random_rewire() functions have been made more consistent.

The object may be globally reset via the seed_rng() function.