Merge pull request #273 from pelson/pcolormesh_warn

Added warning about cmap set_bad.
Merge pull request #283 from pelson/docs

General polish to the cartopy docs
Merge pull request #279 from pelson/mpl1.3

Matplotlib v1.3 support.
Merge pull request #286 from pelson/geo_images

Upgraded the Img class in cartopy.io.img_nest
Added support to project Point and MultiPoint instances.