Add timezone aware snap modifiers

This allows for modifications in the given timezone. ie, snapping to the
beginning of the day with @d uses midnight in the given timezone instead
of in UTC. As usual, the maya object returned is back in UTC, only the
modifications happen in the requested timezone.

README.rst

@@ -92,6 +92,11 @@ Behold, datetimes for humans!
     >>> dt.snap('@d+3h').rfc2822()
     'Mon, 21 Feb 1994 03:00:00 GMT'
 
+	# snap modifiers within a timezone
+    >>> dt = maya.when('Mon, 21 Feb 1994 21:21:42 GMT')
+    >>> dt.snap_tz('+3h@d', 'Australia/Perth').rfc2822()
+	'Mon, 21 Feb 1994 16:00:00 GMT'
+
 ☤ Advanced Usage of Maya
 ------------------------
 

src/maya/core.py

@@ -153,6 +153,17 @@ class MayaDT(object):
         """
         return self.from_datetime(snaptime.snap(self.datetime(), instruction))
 
+    def snap_tz(self, instruction, in_timezone):
+        """
+        Returns a new MayaDT object modified by the given instruction.
+        The modifications happen in the given timezone.
+
+        Powered by snaptime.  See https://github.com/zartstrom/snaptime
+        for a complete documentation about the snaptime instructions.
+        """
+        dt_tz = self.datetime(to_timezone=in_timezone)
+        return self.from_datetime(snaptime.snap_tz(dt_tz, instruction, dt_tz.tzinfo))
+
     # Timezone Crap
     # -------------
     @property

tests/test_maya.py

@@ -383,3 +383,23 @@ def test_snaptime(when_str, snap_str, expected_when):
     dt = dt.snap(snap_str)
     # then
     assert dt == maya.when(expected_when)
+
+
+@pytest.mark.parametrize(
+    "when_str,snap_str,timezone,expected_when",
+    [
+        (
+            "Mon, 21 Feb 1994 21:21:42 GMT",
+            "@d",
+            "Australia/Perth",
+            "Mon, 21 Feb 1994 16:00:00 GMT",
+        )
+    ],
+)
+def test_snaptime_tz(when_str, snap_str, timezone, expected_when):
+    # given
+    dt = maya.when(when_str)
+    # when
+    dt = dt.snap_tz(snap_str, timezone)
+    # then
+    assert dt == maya.when(expected_when)