Also test on Python 3.4
Switch Travis to use tox for testing

Existing travis builds all failed and I'm not inclined to debug them.
Set no ETag on resources when application provides no ETagAdapter

This introduces backwards compatibility with zope.browserresource before
3.11.0 and allows applications not to use ETags and rely on timestamps
instead without having to work around this by adding a NoETagAdapter as
the test does.
Add Changelog entry for GitHub #1