Added tconvert-like command-line interface for gwpy.time
This PR adds a command-line interface to gwpy.time
to replicate tconvert
functionality, used as follows:
$ python -m gwpy.time 1161887657
2016-10-30 18:34:00.000000 UTC
This also improves the functionality of gwpy.time._str_to_datetime
by optionally using maya
to parse datetime strings, its a little better than dateutil
.