The shared options object is now a class attribute of View
The channel options are now a class attribute of SheetOverlay
Fixed a bug in _collapse method of SheetPlot
Fixed constructor of ChannelOpts to allow empty definitions
Fixed __repr__ of ChannelOpts
Introduced unload_python_extension for testing purposes
Python 3 fix for ChannelMagic - string.letters removed in Python 3
Improved IPTestCase and removed deprecated IPHookTestCase
Added docstring instructions to the %%channels cell magic
Added 18 new unit tests for the opts, view and channels magics