errorbar: fmt kwarg default is ''; deprecate None, use 'none' instead

Closes #2366, replaces #2738.
DOC: mention Anaconda; clean some old junk out of the FAQ
DOC : add documentation to Polygon methods

closes #3035
Merge pull request #3123 from tacaswell/polygon_doc

DOC : add documentation to Polygon methods
DOC : added aspect to pyplot.axes doc
DOC : Added link to axes.Axes.set_aspect

Added link to axes.Axes.set_aspect in the docstring
for pyplot.axes
DOC : added inherited-members to Axes autodoc

The re-factor of Axes split the class up into several
classes and the function from `_AxesBase` (such as
`set_aspect`) were not being included in the generated
documentation.
DOC : Added docstrings to _CollectionWithSizes

Added docstrings for get_sizes and set_sizes
DOC : tweaked Collection api auto-doc properties

Include inherited methods (so get_sizes and set_sizes
show up) in auto-doc
DOC : added whats_new entry for _CollectionWithSizes
Merge pull request #3103 from efiring/errorbar_defaults

errorbar: fmt kwarg defaults to None; use 'none' to suppress plot call
Merge pull request #3128 from tacaswell/axes_aspect_doc

Axes aspect doc
Merge pull request #3127 from tacaswell/axes_doc

DOC : added inherited-members to Axes autodoc
Merge pull request #3130 from tacaswell/scatter_set_sizes_whats_new

Scatter set sizes whats new
Merge pull request #3122 from efiring/mention_anaconda

DOC: mention Anaconda; clean some old junk out of the FAQ
BUG : don't use mutable objects as dictionary keys

Base key on the id of the transform.  This maintains
the old behavior and does not break the python hashable
object model.

changed the variable id -> pid so as to not shadow the
method `id`

Closes #2828