Added SkyCoord.to_pixels_wcs
Added test for SkyCoord.to_pixels_wcs
Added a --repeat option for testing
Changes Model.inverse to a property that can be updated to return a custom inverse model when available.  Updates existing models and tests, and adds a test of the new feature.
Fix reference in docstring
Added repeat option to test()
Correctly detect and handle invalid input world coordinates.
Add CHANGES entry
switched to `to_pixel`
add cls keyword to pixel_to_skycoord
Added see also sections
added from_pixel and related tests
Added CHANGES.rst
Fixed docs typo
Fixed typo pointed out by @astrofrog

[ci skip]
Fix to properly include mode parameter

[ci skip]
Fix missing keyword name
Outright removed .invert method per discussion in #3024
Added changelog entry
Typo fix