Now setting the default tz to UTC

If the local tz can not be determined, we now default to
UTC.
Setting default tz to UTC if unable to parse -tz

This fixes the case where we are unable to parse the -tz, and we are
also unable to automatically get the local tz.
Fixing TZ bug in read output

We were using from utctimestamp, but passing in a tz aware
object.  This was causing the time to be printed in utc, but
still appending the specified tz offset.

We're now passing the tz aware datetime to fromtimestamp.  This
results in the specified tz being printed along with the proper
tz offset.
Merge pull request #7 from fiveohhh/set_default_tz

Now setting the default tz to UTC