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/tests/test_timing.py

@@ -0,0 +1,50 @@
+import datetime
+import time
+import contextlib
+import os
+from unittest import mock
+
+import pytest
+from tempora import timing
+
+
+def test_IntervalGovernor():
+    """
+    IntervalGovernor should prevent a function from being called more than
+    once per interval.
+    """
+    func_under_test = mock.MagicMock()
+    # to look like a function, it needs a __name__ attribute
+    func_under_test.__name__ = 'func_under_test'
+    interval = datetime.timedelta(seconds=1)
+    governed = timing.IntervalGovernor(interval)(func_under_test)
+    governed('a')
+    governed('b')
+    governed(3, 'sir')
+    func_under_test.assert_called_once_with('a')
+
+
+@pytest.fixture
+def alt_tz(monkeypatch):
+    hasattr(time, 'tzset') or pytest.skip("tzset not available")
+
+    @contextlib.contextmanager
+    def change():
+        val = 'AEST-10AEDT-11,M10.5.0,M3.5.0'
+        with monkeypatch.context() as ctx:
+            ctx.setitem(os.environ, 'TZ', val)
+            time.tzset()
+            yield
+        time.tzset()
+
+    return change()
+
+
+def test_Stopwatch_timezone_change(alt_tz):
+    """
+    The stopwatch should provide a consistent duration even
+    if the timezone changes.
+    """
+    watch = timing.Stopwatch()
+    with alt_tz:
+        assert abs(watch.split().total_seconds()) < 0.1