ENH cbook is now deprecated and replaced by the private module _cbook
ENH all of matplotlib's module now used _cbook instead of cbook
ENH examples are now using _cbook instead of cbook
Moved _cbook to a utils subpackage
ENH splitted the _cbook module in two: the used methods and the unused methods
ENH matplolib's example now uses the new utils module, instead of the deprecated cbook module
ENH last updates on cbook in the matplolib main codebase (docstrings)
ENH matplotlib toolkits now uses the new utils module instead of the deprecated cbook module