these examples read GRIB files and generate
plots of the data using matplotlib and cartopy

test_spectral.py also uses pyspharm, available from 
http://github.com/jswhit/pyspharm

to run all the tests, run 'python run_tests.py'

to run all the tests and compare
images to archived baselines install pytest-mpl, set
MPLBACKEND to 'agg' and run
'pytest test*py --mpl --mpl-baseline-path=baseline_images'

to regenerate baseline image 'pytest <script> --mpl-generate-path=baseline_images'
(using agg matplotlib backend)
