Integrate more complex cartopy and basemap features

[lukelbd]

This will add integration for some addictional cartopy and basemap features, like Basemap.bluemarble. Should be pretty simple. Just add stuff to the ProjectionAxes.format and CartopyAxes._format_apply and BasemapAxes._format_apply methods.

[bradyrx]

Have you gotten #21 / SciTools/cartopy#1117 to work prior to the formal cartopy update? I know you mentioned in #21 that you could get it to work manually, but I haven't had any success. Curious if you have any hacky ideas to get grid labeling done in proplot.

[lukelbd]

@bradyrx Looks like I missed your comment before -- no I haven't tried it but I assumed it would be fine because I was using the public gridliner API. Maybe the new API contains backwards incompatible changes. I'd prefer to just cross that bridge when I come to it but you can submit a PR if you like.

[lukelbd]

Also, I'm closing this PR since I don't anticipate finishing anytime soon. Will just leave #36 open and if someone is super motivated to have map scales, etc. they can open their own before I get to it. And adding support for the new cartopy gridliner API would be a matter for a different PR.