More PEP8, dead code removal, improve tests

Update docs concerning last pywcs reference
Mark astropy as required in docs
Close files opened by pyregion.open
Obliterate Kapteyn code. Leave no survivors.

Add docs and tests to the Kapteyn-less methods
Addresses #43 and #44, fixes #35
Remove broken rot_wrt_axis parameter for now

I'm convinced the current handling (and previous default) is wrong
Reference to format is provided