Place Grapher in Visualization document
Weave visualization module

The visualization module is now woven (for lack of a better phrase) into
a literate document.
Fix interpretation issues

See diff of org for details.  Basically, you cannot refer to a static
member of the class before the class block has been defined; therefore a
default value of `Grapher.plain_node_painter` doesn't work.
Fix widget resizing and add test
Implement static layout

When resizing the widget, it's unlikely that 're-layout' is desired as
well.  This commit separates that functionality through the use of a
`do_layout` flag to `paint` that defaults to `True`.
Prototype animator
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Simplify enqueue logic
Use sparse graph instead of complete graph
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Begin consolidation
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Explain *why* this is a bad thing
Fix README
Roadmap
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fix link
:(
Branch descriptions
Pull final.py into document