1.9.9 plot_net: faster, more-flexible network plot

CHANGES IN VERSION 1.9.9
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USER-VISIBLE CHANGES

	- `plot_net` faster, more-flexible network plot with improved defaults
1.9.9 NEWS added pull request link
Merge pull request #353 from joey711/update-plot_network

1.9.9 plot_net: faster, more-flexible network plot