Notable changes in 0.32 since 0.31

Python 3 is now preferred. Python 2 support is deprecated, and it's possible that we'll stop new development for Python 2 fairly soon. If so, we'll probably continue to fix bugs in the last Python 2 compatible version for a while, but please make plans to migrate.

At the moment, ./configure doesn't explicitly look for any python newer than python3.8 by default (though one might be selected by the eventual python3 fallback). If desired, you can explicitly select a version like this:
```
PYTHON=python3.9 ./configure
```
With Python 3.9, the command line reported in tools like ps and top will be python... rather than bup.... This was caused by an upstream change that appears to have been reverted. We're likely to avoid the issue entirely in a future relese.

Bugs

A number of Python 3 compatibility problems have been fixed.
bup web should no longer crash when attempting to listen on IPV6 interfaces.
bup restore -vv should no longer crash when printing paths with Python 3.
bup --prune-older --pretend should format the plus/minus lines correctly now.
The TTY_WIDTH should now be correctly propagated to subprocesses and remotes..
Errors encountered while writing packfiles should be handled more carefully.
Some issues with the handling of integral type signs and sizes on the C side have been fixed.

The tests are now handled by pytest. See the README for the additional dependency information and further instructions.

Christian Brabandt, Greg Troxel, Gustavo Goretkin, Jean-Paul Marmorat, Johannes Berg, Karl-Philipp Richter, Rob Browning, and danpawlik