Upgrade GeoTIFF export.

Add support for various data types.
Add support for coord systems.
Map 0 to 360 longitudes into the -180 to 180 range.
Merge pull request #750 from rhattersley/fix-geotiff

Fix GeoTIFF export
ENH: Completed whatsnew for v1.5
Merge pull request #755 from cpelley/whatsnew

(Almost) final version of what's new for 1.5.

Just needs a release date.
Merge remote branch 'upstream/v1.5.x'

 - #750 Upgrade GeoTIFF support.
 - #755 Update what's new for 1.5.