This pull request introduces a new plotting backend for HoloViews based on the bokeh library. Bokeh provides support for a lot more interactivity, allows for faster rendering and should help us develop our goals towards dynamic rendering of large amounts of data.
The actual backend implementation shares largely the same API as matplotlib in terms of plot options and some effort has been made to convert between matplotlib and bokeh options. A number of things are not yet implemented (in holoviews) or are unsupported (by bokeh):
However I believe it is ready to be merged and can be improved and extended over time. This will allow users to try it out and report bugs before a next release.
Removes need to implement custom get_extents for Spread Element