Standardize how Python version checking is done.
Add changes to io.fits
Make `@deprecated` decorator work for classes.
Fix pickling issues with class deprecation.  Fix Python 2.6 bug.
distance > 0
now with optional kwarg allow_negative
added test of new kwarg
added note in coordinates docs about negative distances
update error message
added line about distance change to changelog
Merge pull request #2118 from adrn/distance

Distance should never be < 0 (unless explicitly allowed)
Add CHANGES section for 0.3.2
Merge pull request #2188 from astrofrog/changelog-0.3.2

Add CHANGES section for 0.3.2
 Fix #2173: axis keyword in median_absolute_deviation.

The axis keyword in median_absolute_deviation is now taken into
account for any axis, and the data properly broadcasted.  The
corresponding unit test is updated.
Merge pull request #2156 from mdboom/misc/deprecating-classes

Make `@deprecated` decorator work for classes.
Merge pull request #2143 from mdboom/misc/version-standardization

Standardize how Python version checking is done.
Merge pull request #2191 from evertrol/fix_2173

 Fix #2173: axis keyword in median_absolute_deviation.
Added Wien wavelength displacement law constant.
Merge pull request #2194 from pllim/wien-disp-const

Added Wien wavelength displacement law constant
Added Redshift model for wavelength.