Assume templates/ is relative to $PWD/

This is needed in order that pyprof2calltree works, because when
we run the profiler, __main__ is not our module but the profiler,
which screws up the path finding.
Disable broken test

This test was broken when we modified the get_tables implementation.

Disable it for now.
Memoize column escaping

This is a quick win, albeit a relatively small one.
Use requests_cache if USE_REQUESTS_CACHE is nonempty
Use os.path.join
PEP8ify
Add negative TZ test