Make astropy.io.registry and astropy.io.misc compatible with Python 2 and 3 using six
Avoid double copy of data in registry
Added future imports
Use zip from six to avoid duplicate copy of data in memory
Added new Sphinx extension to auto-link issue numbers
Whitespace
As suggested by @embray, make issue linking for robust by first searching for groups of issues that are enclosed in square brackets and have the form [#...], then cycle over the issues inside each group.
Make issue block matching less strict
Fixed Gaussian2D model
Stored several calculations for reuse
insert spaces around all operators for internal consistency
updated changelog
updated changelog
Added new Gaussian2D model test
doc fixes
added new Gaussian2D model test
updated Gaussian2D test
Allow TimeDelta to have (well-defined) scales other than TAI
Ensure UTC times can be used in arithemetic with Quantity; add UT1 for TimeDelta
Change dict comprehension for python 2.6