allow case-sensitive env vars
Update installation.rst

Update compatibility notes regarding ZeroMQ versions and add detail about how this is determined by pyzmq dependency.
Oops.  Fix rst link syntax.
Add caveat about PyPy.
Merge pull request #741 from eikonomega/master

Update installation docs with more details on zeromq version support.
Use text_type instead of str to handle unicode.
Merge branch 'case-sensitive-cfg' -- Allow case sensitive environment variables
add TimedRotatingFileStream