Starting 0.4, config.py->version.py.
Convert astropy's Header instances for kapteyn.
Use skiptest_unless_module header in test_wcsutils.py.
Rename observation -> configuration.
nvertices should not be a class attribute.
Some cleanup.
Make the coordinate conversion routines private.
matplotlib.pyplot as mp.
Fix 1-based kapteyn convention in Configuration.plot. Cleanup.
Add Imager class. Remove detector_center & detector_vertices from Instrument's __init__.
Style.