version 1.0.6:  Added drawcounties,arcgisimage methods. 
version 1.0.5:  Added 'latlon' keyword to plotting methods (converts lat/lon to x/y
                and shifts data in longitude (using shiftdata method) to map projection region.
version 1.0.3:  Added streamplot method.
version 1.0.2:  default value for lakes kwarg in drawlsmask changed from False to True.
                default value for inlands kwarg in maskoceans changed from False to True.
                NetCDFFile function removed.
version 0.99: now must be imported as mpl_toolkits.basemap instead
              of matplotlib.toolkits.basemap.
version 0.9.8: remove linestyle kwarg from drawparallels and drawmeridians.
               add fill_color kwarg to drawmapboundary.
version 0.9.7: added lake_color kwarg to fillcontinents.
version 0.9.6: added "labelstyle" keyword to drawparallels and drawmeridians.
               added "zorder" kwarg to drawparallels, drawmeridians,
               drawcoastlines, drawstates, drawcountries, drawrivers,
version 0.9.2: width, height keywords added to Basemap.__init__.
version 0.9.1: createfigure method removed.
version 0.9: creatfigure method deprecated, new set_aspect axes method
             used to ensure maps have right aspect ratio. 
             pcolormesh, drawlsmask methods added.
version 0.7.2:  'createfigure' method added to Basemap.
                interp function no longer uses nd_image, so keywords
                'mode' and 'cval' no longer accepted.  'order' keyword
                must be 0 or 1.
version 0.7.1:  'readshapefile' method added to Basemap.
version 0.5.2:  'ax' keyword added to Basemap.__init__. This well set
                default axis instance, which can be overridden by using
                'ax' keyword in method calls.
version 0.5.1: 'font' and 'fontsize' keyword args for drawparallels and
               drawmeridians replaced by **kwargs, which is passed directly
               to Axes text method. Most Basemap methods now take keyword
               argument 'ax' to allow use of a pre-existing Axes instance
               (default is to use current instance).
version 0.5: llcrnrlon,llcrnrlat,urcrnrlon,urcrnrlat are now optional
             keyword paramaters in Basemap.__init__,
             'xoffset', 'yoffset' optional keyword args added to
             Basemap.drawparallels and Basemap.drawmeridians.
             added optional 'suppress_ticks' keyword arg to Basemap.__init__.
version 0.4.2:  removed 'preserve_magnitude' keyword from transform_vector.
version 0.3:  axes instance no longer an argument to any Basemap method.
              (gca is called to obtain the current axes instance instead).