matplotlib Code

Added hexbin axes method and pyplot function by Michiel de Hoon.
Tracker 1952339.

fixed an aspect=auto problem with bezier ellipse approx

Factored plotting part of pylab.py into pyplot.py

Added step plot based on patch by Manuel Metz

Removed last vestiges of old pcolor, scatter, quiver versions.

minor modernization

added xcorr and acorr plot functions

Moved pylab._shift_string() to cbook.dedent() to facilitate its use

added tims spectral patch

Replace old spy and spy2 with new spy (briefly called spy3)