Merge branch 'feature-gtiff-overviews' into 'master'

Add overviews to geo2grid geotiffs and fix transparency in mapserver

See merge request cspp_geo/cspp-geo-web-viewer!13

mapserver/mapfiles/g16_abi_radf_l1b.map

 MAP
   NAME "GOES-16 ABI Full Disk L1b Layers"
   STATUS ON
-  IMAGETYPE      PNG
-  SIZE           256 256
+  IMAGETYPE rgba
+  SIZE 256 256
   EXTENT -5434894.885 -5434894.885 5434894.885 5434894.885
   #EXTENT         -180 -90 180 90
   
@@ -18,6 +18,7 @@ MAP
     END
   END
 
+  INCLUDE '/work/mapfiles/output_formats.map'
 
   ##############
   # True Color #