Python: added repr() support for astronomy.Time class.

Now when a Time object is evaluated and represented in
the Python interpreter, it results in a string of the form:

    astronomy.Time(ut)

where ut is the numeric representation of the ut field.
This mimics the exact way such a Time value could be constructed.
That is, eval(repr(t)) results in a time value equal to t.

source/python/astronomy.py

@@ -553,6 +553,9 @@ class Time:
         """
         return Time(self.ut + days)
 
+    def __repr__(self):
+        return 'astronomy.Time(' + repr(self.ut) + ')'
+
     def __str__(self):
         millis = round(self.ut * 86400000.0)
         n = _EPOCH + datetime.timedelta(milliseconds=millis)