Add expand_to_include method to gdal Envelope

[psmith]

Mapnik has an Envelope class like that in django.contrib.gis.gdal.envelope that ​has an expand_to_include method we should steal. This is handy for building up an envelope by iterating over a collection of geometries -- at the end you have the extent / envelope of the collection.

>>> e = Envelope(pt_list[0])
>>> for pt in pt_list[1:]:
...     e.expand_to_include(pt)

or

>>> e = Envelope(geom_list[0].extent)
>>> for g in geom_list[1:]:
...     e.expand_to_include(g.extent)

[psmith]

Patch to add expand_to_include to Envelope (with unit tests)

[jbronn]

(In [9985]) Maintenance refactor of the GDAL (OGR) ctypes interface. Changes include:

• All C API method explictly called from their prototype module, no longer imported via *.
• Applied DRY to C pointer management, classes that do so subclass from GDALBase.
• OGRGeometry: Added from_bbox class method (patch from Christopher Schmidt) and kml property.
• SpatialReference: Now initialize with SetFromUserInput (initialization is now more simple and flexible); removed duplicate methods.
• Envelope: Added expand_to_include method and now allow same coordinates for lower left and upper right points. Thanks to Paul Smith for tickets and patches.
• OGRGeomType: Now treat OGC 'Geometry' type as 'Unknown'.

Fixed #9855, #10368, #10380. Refs #9806.