[+ util/benchmark_gti] test "slow" bit of parser
[benchmark_guess_ts_info] use timeit module
[ts.parse] rename guess_timestream_info
[ts.parse] logging and write out guessed manifest

now we call LOG.debug and LOG.warn in a few more places where recording
stuff like that might be interesting. WARNING: setting a handler to
DEBUG level is now likely to produce quite a lot of guff. Perhaps use
INFO unless you really are debugging.

Also, we now try (and silently fail) to write a JSON representation of
the manifest to disk, so we don't end up re-guessing it. Not that that
would hurt.
[ts.parse] fix up strf/strptime wrappers
[ts.parse] refactor so module names are consistent
[ts.parse] implement get_image - get image by date

This function gets a single image by date from a timestream