Support albers_conical_equal_area projection

[rsignell-usgs]

This attempt to get a Cartopy crs from a CF-compliant dataset:

import xarray as xr
import metpy
url = 'http://geoport.usgs.esipfed.org/thredds/dodsC/sand/usgs/users/rsignell/data/testing/albers.nc'
ds = xr.open_dataset(url)
ds = ds.metpy.parse_cf()
crs = ds['facies_class'].metpy.cartopy_crs

yields:

ValueError: Unhandled projection: albers_conical_equal_area