Added rplot stub
Added an RPlot class and a simple geom class
Added GeomDensity2d
Small improvements
Set colours from a column
Added a docstring to filter_column
Added parse_facets function
Work on layer class
Added docstring to scale_size function
Added scale_gradient function
Added scale_gradient function
Added a test function to display grouped plots
Added TrellisGrid class
Added scale_constant function
Added scale_gradient2 function
Added scale_shape function
Adjust spacing and axis limits in trellis plots
Display shingle variable values in a matplotlib table
Redefined GeomPoint class
Removed an unused function