Palettable

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* The ``print_maps_by_type`` and ``get_map`` functions are now insensitive
to the case of the ``map_type`` parameter.
* The ``get_map`` function is now insensitive to the case of the name parameter.
* Fixed a bug in ``get_map`` that caused color maps not to get reversed
when they should have been.
* Added a test suite.

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* Removed the ``number`` parameter from ``BrewerMap`` construction. This attribute
is now set from the length of the ``colors`` input.
* Added the ``BrewerMap`` class to the list of names imported in the brewer2mpl
namespace. This will make it easier for users to make their own color maps
by mixing and matching existing ones.