Removing deprecated code
Removing import of spectrum1dlinearWCS
Fixing BSplineModel
Fixing BSpline, LoopupWCS, and polynomialWCS
Fixing weightedCombinationWCS, CompositeWCS, and DopplerShift models
Adding LOG and Doppler WCS for linear and log-linear readers
Adding support for linear reader and writer and adding test for for writer
Using composite models and the new design of MultispecIRAFCompositeWCS to implement reader for multispec format
Rebasing on top of the model framework, and updating readers and writers to use this framework
Adding test case for linear reader
Converting spec2 to log-linear dispersion type