some minor modifications
updating the imports and updating to the new model class.
first go at implement @iguananaut's new modeling API into specwcs.
added the new astropy API to specwcs lookup model
updates specwcs to @embray's new model API.
some minor bugfixes
Merge branch 'master' into specwcs_update

Conflicts:
	specutils/wcs/specwcs.py
Merge pull request #36 from wkerzendorf/specwcs_update

specwcs update to new modeling API