Raise exception when user tries to use set_xlim or set_ylim on a geographic projection

[adrn]

This is a pretty simple, atomic change but may require some documentation if accepted. I've found that when teaching users about projections, many people expect to be able to change the projection limits (rotate the projection) by using set_xlim() and set_ylim(). The functions work on projection axes:

>>> fig,axes = plt.subplots(1,1,subplots_kw=dict(projection="aitoff"))
>>> axes.set_xlim(0,360)

but don't actually do anything. I propose (with this PR) that these functions explicitly throw a NotImplementedError so it is obvious to the user that they are not actually changing anything by using the limit functions:

>>> axes.set_xlim(0,360)
NotImplementedError: set_xlim and set_ylim are not implemented for geographic projections

[dmcdougall]

I'm happy with this approach. We should be clear when the user does something wrong, and this achieves that. I would rather the error message be a little more self-explanatory. Perhaps something like,

NotImplementedError: It is not possible to change axes limits for geographic projections

Also, maybe it makes more sense to raise a TypeError to really get across that it's the type of projection that doesn't support this behaviour.

[adrn]

Sure, that seems reasonable to me! Will make changes and commit.

[WeatherGod]

I would consider this a bug of sorts. Maybe this is more the realm of
basemap, but not being able to change the limits would be a major turn-off
to me. At the very least, perhaps we should have the message point users
to basemap?

[mdboom]

👍

[pelson]

If you add "Please consider using Basemap or Cartopy." to the exception, I think this is good to go.

[pelson]

Merged with e528dad.

Thanks @adrn.