* Refactoring AxisText to be backend independent. Text drawing and
get_window_extent functionality will be moved to the Renderer.
* backend_bases.AxisTextBase is now text.Text module
* All the erase and reset functionality removed from AxisText - not
needed with double buffered drawing. Ditto with state change.
Text instances have a get_prop_tup method that returns a hashable
tuple of text properties which you can use to see if text props
have changed, e.g., by caching a font or layout instance in a dict
with the prop tup as a key -- see RendererGTK.get_pango_layout in
backend_gtk for an example.
* Text._get_xy_display renamed Text.get_xy_display
* Artist set_renderer and wash_brushes methods removed
* Moved Legend class from matplotlib.axes into matplotlib.legend
* Moved Tick, XTick, YTick, Axis, XAxis, YAxis from matplotlib.axes
to matplotlib.axis
* moved process_text_args to matplotlib.text
* After getting Text handled in a backend independent fashion, the
import process is much cleaner since there are no longer cyclic
dependencies
* matplotlib.matlab._get_current_fig_manager renamed to
matplotlib.matlab.get_current_fig_manager to allow user access to
the GUI window attribute, e.g., figManager.window for GTK and
figManager.frame for wx
