Initial python3 changes

Mostly just updating libraries, removing string encoding/decoding,
fixing some edge cases. No new functionality was added in this
commit.

lib/tempora/utc.py

@@ -0,0 +1,36 @@
+"""
+Facilities for common time operations in UTC.
+
+Inspired by the `utc project <https://pypi.org/project/utc>`_.
+
+>>> dt = now()
+>>> dt == fromtimestamp(dt.timestamp())
+True
+>>> dt.tzinfo
+datetime.timezone.utc
+
+>>> from time import time as timestamp
+>>> now().timestamp() - timestamp() < 0.1
+True
+
+>>> (now() - fromtimestamp(timestamp())).total_seconds() < 0.1
+True
+
+>>> datetime(2018, 6, 26, 0).tzinfo
+datetime.timezone.utc
+
+>>> time(0, 0).tzinfo
+datetime.timezone.utc
+"""
+
+import datetime as std
+import functools
+
+
+__all__ = ['now', 'fromtimestamp', 'datetime', 'time']
+
+
+now = functools.partial(std.datetime.now, std.timezone.utc)
+fromtimestamp = functools.partial(std.datetime.fromtimestamp, tz=std.timezone.utc)
+datetime = functools.partial(std.datetime, tzinfo=std.timezone.utc)
+time = functools.partial(std.time, tzinfo=std.timezone.utc)