DotPipe/GraphvizLayoutPipe

[nrbgt]

While it has a lot of warts, the graphviz text format is:

• widely supported as an output of many tools
• powerful enough to enumerate a pretty large subset of constructs
  • ports are ugly though, and require the HTML-ish syntax
• extremely forgiving, to the point of being live-editable

On the one side, having a Pipe that:

• on run, used pygraphviz (not a lightweight dependency)
  • take as source a slug of text/graphviz
  • emit a value of the equivalent networkx graphs

And on the other:

• used networkx.draw to do the classic implementations to get mark locations

Would offer a lot of ready-to-test values, and make for some nice demos.

References:

• blocked by overhaul top level interface #89