As requested in https://github.com/zopefoundation/meta/issues/116

* Document deprecation of this package.
* Document suggested alternatives.
* Warn at runtime about the deprecation status of the package so developers using it can get a hint even when they don't read the readme of this package.

Document deprecation of this package.

Apply suggestion
Co-Authored-By: Michael Howitz <mh@gocept.com>

* fix RuntimeError in py3
* move test requirements from tox.ini to setup.py

[skip ci]

modified:   .travis.yml
modified:   CHANGES.rst
modified:   setup.py
modified:   tox.ini

modified:   .travis.yml
modified:   CHANGES.rst
modified:   setup.py
modified:   tox.ini

cf https://docs.travis-ci.com/user/languages/python/#pypy-support

This closes #9.

modified:   .travis.yml
modified:   CHANGES.rst

... by installing an updated setuptools version.

modified:   .travis.yml

This prevents a KeyError: '\x00\x00\x00\x00\x00\x00\x00\x00'

Removed doubt-inducing version pins

fixed a bug in loadBefore

I guess there were no tests of GC.

That was made effective by recent changes in ZODB that relied more on
loadBefore for MVCC.

Oddly the change makes this loadBefore match the version it was copied
from, which github says was last changed 13 years ago. (gulp, on
multiple levels).

Test on pypy3 as well