Add the Strebe 1995 projection

[Veeno]

The title says it all for this feature request. Strebe 1995 is an equal-area projection with unique properties which I would really like to see added to cartopy.

[dopplershift]

Cartopy relies upon the PROJ library (specifically the PyPROJ wrapper) for all of its projections. I wasn't able to find the projection in there with a quick search. If it actually is present in PROJ, then adding it to Cartopy should be a straightforward PR; if not, someone would first need to add it to PROJ.

[Veeno]

Indeed, it isn't included in PROJ's available projections. I will create an issue on the PROJ repository.