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).