This updates all Python packages that download their source from PyPi to
use pypi.mk.

This will allow future improvements/changes to pypi.mk to affect all
relevant packages.

This also makes it easier for future Python packages to start using
pypi.mk, when it's clear how it is used in existing packages.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

This updates the Python 2 and 3 versions of each package to share the
same title field. (For packages that only had this change, their
PKG_RELEASE were not incremented.)

This also updates the package title, url and source urls, where
necessary.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>

This is a new requirement for the Twisted package.

From the readme:

Incremental is a small library that versions your Python projects.

Signed-off-by: Jeffery To <jeffery.to@gmail.com>