Fix tests w/o zope security

Add a new testrunner, 'test-wo-zope-security', to exercise the 'skipUnless'
added in d910979a.

Fix removing pure python security proxies

The test is simple but requires zope.security to be installed.
I chose that over writing the test in zope.security

Don't use/poison global wheel cache when building w/ PURE_PYTHON.

Drop support for Python 2.6 and 3.2.

Use shields.io for PyPI badge

Note explicit support for Python 3.5

Make subclasses of ProxyBase delegate __module__ to the wrapped object. Also fix differences between the C and Python implementations in handling __module__, whether or not a subclass is involved.

Merge branch 'int-and-float' of git://github.com/NextThought/zope.proxy into NextThought-int-and-float

Handle descriptors defined in PyProxyBase subclasses like C

Python 2.6 uses a "hack" to call __complex__ and so we lost coverage of that. 2.7 does it correctly. See https://github.com/zopefoundation/zope.proxy/pull/6#issuecomment-103618850

Make it easier to subclass PyProxyBase using multiple-inheritance. This will let zope.container._proxy reuse all the fixes in this branch.

Make the C implementation proxy __unicode__, and make it use the standard methods to proxy int and float. Fixes #3 and Fixes #4.

Handle descriptors defined in PyProxyBase subclasses the same way the C version does. This fixes #5.