This module is a polyfill, implementing ChainMap for reasonably-recent versions
of Python that do not have collections.ChainMap--namely, Python 2.6, Python 3.2,
and PyPy3 releases based on Python 3.2. (It will also work as expected on Python
2.7, PyPy, and Python 3.3 and higher, but it is not needed there since those
verions' collections modules contains a ChainMap implementation.)

The code for this package is closely derived from the Python 3.5 source code at
hg.python.org, (especially the collections and reprlib modules). Several changes
have been made to ensure Python 2.6 compatibility, and tests and packaging have
been added.