added first quantity support to the extinction functions
removed range check for interpolation functions. added tests for out of range values.
changed the cython exctionion name to cextinction as it should be available to the users.
fixed multidimensionality for the ccm89, restructured functions for ccm89.
implementing various fixes - tests don't pass yet.
restructuring the extinction classes to models
added test for fm07
fixed small testing bug
updated testing to include the extinction function.
finished conversion to models
Merge pull request #1 from wkerzendorf/extinction/update

Extinction update to Quantities