`.SymLogNorm` now has a *base* parameter

Previously, `.SymLogNorm` had no *base* kwarg, and defaulted to ``base=np.e``

whereas the documentation said it was ``base=10``. In preparation to make

the default 10, calling `.SymLogNorm` without the new *base* kwarg emits a

Previously, `.SymLogNorm` had no *base* keyword argument, and

defaulted to ``base=np.e`` whereas the documentation said it was

``base=10``. In preparation to make the default 10, calling

`.SymLogNorm` without the new *base* keyword argument emits a

deprecation warning.

The *colors* parameter will now default to:rc:`lines.color`, while previously it defaulted to 'k'.

Aggressively autoscale clim in ``ScalerMappable`` classes

Previously some plotting methods would defer autoscaling until the

first draw if only one of the *vmin* or *vmax* keyword arguments were

passed (`.Axes.scatter`, `.Axes.hexbin`, `.Axes.imshow`,

`.Axes.pcolorfast`) but would scale based on the passed data if

neither was passed (independent of the *norm* keyword arguments).

Other methods (`.Axes.pcolor`, `.Axes.pcolormesh`) always autoscaled

base on the initial data.

All of the plotting methods now resolve the unset *vmin* or *vmax*

at the initial call time using the data passed in.

If you were relying on exactly one of the *vmin* or *vmax* remaining

unset between the time when the method is called and the first time

the figure is rendered you get back the old behavior by manually setting

the relevant limit back to `None` ::

which will be resolved during the draw process.

"vmin/vmax directly to the norm when creating it.")

else:

self.autoscale_None()

self.autoscale_None()

defto_rgba(self,x,alpha=None,bytes=False,norm=True):