Implements rendering of HeatMapSeries with rectangles (#801)
Implements rendering of HeatMapSeries with rectangles (#801)

Only employed when Interpolate is set to false, and RenderDiscreteRectangles is set to true

Kaplas80/oxyplot,shoelzer/oxyplot,objorke/oxyplot,Kaplas80/oxyplot,ze-pequeno/oxyplot,zur003/oxyplot,objorke/oxyplot,shoelzer/oxyplot,HermanEldering/oxyplot,shoelzer/oxyplot,oxyplot/oxyplot,DotNetDoctor/oxyplot,Isolocis/oxyplot,objorke/oxyplot,olegtarasov/oxyplot,NilesDavis/oxyplot,DotNetDoctor/oxyplot,olegtarasov/oxyplot,HermanEldering/oxyplot,Jofta/oxyplot,Jonarw/oxyplot