fixed up the dispersion attribute handlers
update to @keflavich's equivalencies - furthermore update to `Legendre1D`.
Marked SFD98 test as xfail
Merge pull request #43 from jfoster17/master

Test the O'Donnell 1998 extinction law against SFD98
fixed up the dispersion attribute handlers
update to @keflavich's equivalencies - furthermore update to `Legendre1D`.
adding wcs information grabber
added `FITSWCSSpectrum` fits keyword parser.
two readers are implemented using the information class.
deleted fits reader in wcs.
this was the last link to fits in specwcs for now.
added ordered dictionary for the WAT keywords according to @mhvk's suggestion.
Merge pull request #44 from wkerzendorf/fix_spectrum1d_attributes

Fix spectrum1d attributes
Merge pull request #41 from wkerzendorf/fits_wcs_cleanup

FITS WCS cleanup
added a Spectrum1D polynomial model
deprecated Spectrum1DLinearWCS
added Spectrum1D Polynomial to the fits_reader. Also added shape to the FITS keyword header reader.
skipped failing tests - both readers and testers will have to be reimplemented using the specwcs classes.
Merge pull request #45 from wkerzendorf/wcs_linear1d2polynomial

convert LinearWCS to Polynomial model
removing non-convertible wcs attributes and lookup_table caching mechanisms (thereby also removing one of @keflavich's concerns.
fixing up attributes stuff
remove unit requirement from lookuptablewcs.