move `diffpy.srfit.sas` to `diffpy.cmisas.sas` in a different repository

[sbillinge]

Problem

This is part of the process of making packs instead of embedding sub-packages in here

Proposed solution

steps might be:

1. create diffpy.cmisas repo on github if it is not already there (simon has to do this....let him know if it is needed)
2. move over all the files there and do the things to create a pack
3. test the pack works like it did before
4. deprecate the diffpy.srfit.sas behavior in case anyone is using it.