Provide a stable and consistent sort order for Range objects.

This matches postgres server-side behaviour and helps client applications that need to sort based on the primary key of tables where the primary key is or contains a range.
Coding style changes.
New implementation of Range sorting that works for Python 2.5 to 3.3, at least.
documentation changes now that Range objects can be ordered
Added str() for the Json adapter

Fixes ticket #191.
Added implementation for Range gt and ge operators

Using a common implementation for all the operators. Note that lt is the
one used by sort so it's nice it's the fastest.
Hardcode the list of attributes to be used in comparison

Comparing Range subclasses may lead to surprises.
Docs wordsmithing about Range order
Mention Range order in the news file
Fixed error message on range parsing failed
Merge branch 'range_sort'