Adding Doppler, LOG and identity WCSes
Changing doppler and log models, and adding Composite and WeightCombination models
Adding class methods to doppler wcs
Removing Log WCS, adding documentation
Adding tests, and fixing an assignment bug
Changing doppler WCS, and adding classmethod for iraf doppler factor
Removing iraf doppler factor and adding inverse method to doppler shift model
Changing the deisgn of doppler wcs
Shifting computation to from_doppler_factor class method, fixing tests
Merge pull request #87 from shaileshahuja/doppler-log-wcs

Adding Doppler, LOG and identity WCSes