Changed and fixed cov2corr
Merge pull request #159 from adonath/cov_to_corr

Changed and fixed cov2corr
Adds main npred cube script to spectral_cube core.py
Adds unit test scripts for spectral_cube npred methods
Adds main rst script for a tutorial for the npred cube methods
Adds plotting scripts for the npred method tutorial

Modified plotting script
Adds Fermi Science tools reference to references.txt file
Begins implementation of image from source catalog script
Adds initial code
update
update
Merge branch 'npred_cube2' of https://github.com/ellisowen/gammapy into image_from_catalog
updage