Added WCS wrapper that implements _as_mpl_axes
Change docs to use simpler ``projection=`` interface
Updated image tests to use new API
Added separate section on initializing WCSAxes since there are now a number of ways.
Fixed bug in angle formatter/locator
Fixed tests
Implemented @cdeil’s comments
Fix first example in docs
Merge pull request #136 from astrofrog/wcs-wrapper

Make use of Matplotlib's projection= framework