add colorbar method

Author: Jeff Whitaker

Changelog

@@ -1,4 +1,6 @@
 version 1.0.2 (not yet released)
+           * added colorbar method that uses axes_grid toolkit to
+             create colorbar axes.
            * replace hasattr(arr,'mask') with numpy.ma.isMA(arr).
            * docs updated, moved to matplotlib.github.com/basemap.
            * added optional 1.25, 2.5 and 10 minute land/sea masks (derived from