Adds circle support to spread
Merge branch 'master' into feature/ar_recipies
WIP: NoUpdate return message
First working draft of skipped server update when render parameters are unchanged
make toolbar visibility toggleable
Balance zoom only used in initial calculation.  Fixes #1114
Resiliant to lack of render state
Recipies for hdalpha and heatmap.
Used the Bar chart as a starting point for heatmap.
plumbing for multi-range/axis
no longer need to pass ranges to glyphs
Completed a simple HeatMap implementation. Also added examples.
working twin axis example
Made the color mapper more generic.
Now supporting palettes.
fix up add_glyph call missed earlier
update tests
Avoid grids in some categorical charts.
Removed checkpoint folder.
fix copy-pasta update error