Merge pull request #317 from pelson/pcolormesh_masked

Caught case where the pcolormesh has masked pcolor values.
Added Mercator (EPSG:3395) projection, with review actions fixed.
Merge pull request #324 from dkillick/ImprovedMercator

Improved Mercator projection
Fixes necessary for good geolocation of Google map tiles.
ll tests now passing.