First hacky pass at making solar coordinates work.
Dirty 180deg coordinate wrap fix.
Read the transform graph to populate possible WCS coordinates output.
Add HelioGraphicStonyhurst to supported WCS systems for fun!
Tidy up sunpy stuff.
Bug fix for FBrowser plugin
Roll up of small changes

- updated installation docs
- fixed video example for recent changes to opencv
- added an option to Mosaic plugin for mosacing multi-hdu images
- updates to matplotlib backend
Merge branch 'sunpy_coords' of https://github.com/Cadair/ginga into Cadair-sunpy_coords
Fixed bug in image overlays

- also added support for alternate image loaders in Thumbs plugin