CoordinateGrids can now be overlaid with each other
Minor fixes to docstring and exception message
Added label parameter to ViewOperations
ViewOperations can now process CoordinateGrids as input
Channel processing of overlays now in OverlayPlot abstract class
Added channel processing support to CoordinateGridPlot
Simplified constructor of CoordinateGridPlot
Fixed bug in  _collapse when overlays contain duplicate labels
SheetView.normalize can now 'ignore', 'warn' or 'raise' on ZeroDivision
The channel_modes dictionary has been moved to operations on ChannelOpts
Introduced the chain ViewOperation
Introduced the operator ViewOperation