Removed Distance methods unneeded with Quantity
change Distance to proper Quantity subclass
fixes based on broken tests
Make cartesian transform compatible with Distance as Quantity
More tests and related fixes
Implemented `distmod` in Distance
Documentation tweak
fix for unicode literals by changing to six.u
Add extra note in changelog as suggested by @mdboom
Merge pull request #1472 from eteq/distance-to-quantity-2

Change Distance to be a quantity subclass
Merge pull request #1481 from mdboom/docs/six-recommendations

Add information about moving to `six`
Only include easy conversion members on subclasses of Quantity that opt-in.