timezones.pyx has no other dependencies within pandas, helping to de-tangle some of the _libs modules

Code im timezones is used in both tslib and period, and a bit in index.pyx

This is one of several steps in making _libs.period not need to import from non-cython code and
ideally not need to import tslib (though NaT makes that tough).  See existing comments
in _libs.__init__ on why this is desireable.

This is the first of several independent pieces to be split off of tslib.

Cleanup commented-out code

…ndas into tslibs-timezones

Wild guess that it might be causing the build fail on appveyor

…ndas into tslibs-timezones

…ndas into tslibs-timezones