Specify graph plot with x=[.....] and y=[.....]

[BruceSherwood]

Currently, graphing data must be given in the form [ [x,y], [x,y], .....], but many well-known graphing packages require data to be provided in the form x=[.....] and y=[.....], and it has been requested to support this scheme. It is actually the case that both the Flot and Plotly graphing packages supported by VPython use the x and y forms, and VPython reformats the [x,y] form into the x and y form. The relevant file is lib/glow/graph.js.