Fraction: Python operators, formatter

- Equivalents of operator* and operator/ templates are provided
  by implemening `__mul__`, `__rmul__`, __truediv__`, `__rtruediv__`
  in Python code for `openshot.Fraction` class
- An implementation of `__format__` is also provided, allowing
  numeric format strings to be used directly on Fraction objects,
  e.g. `v = Fraction(3, 9); print(f"{v:0.3f}")  # prints '0.333'`

bindings/python/openshot.i

@@ -209,6 +209,31 @@
 		def values(self):
 			_items = self.GetMap()
 			return _items.values()
+		def __mul__(self, other):
+			if isinstance(other, Fraction):
+				return Fraction(self.num * other.num, self.den * other.den)
+			return float(self) * other
+		def __rmul__(self, other):
+			return other * float(self)
+		def __truediv__(self, other):
+			if isinstance(other, Fraction):
+				return Fraction(self.num * other.den, self.den * other.num)
+			return float(self) / other;
+		def __rtruediv__(self, other):
+			return other / float(self)
+		def __format__(self, format_spec):
+			integer_fmt = "bcdoxX"
+			float_fmt = "eEfFgGn%"
+			all_fmt = "".join(["s", integer_fmt, float_fmt])
+			if not format_spec or format_spec[-1] not in all_fmt:
+			  value = str(self)
+			elif format_spec[-1] in integer_fmt:
+				value = int(self)
+			elif format_spec[-1] in float_fmt:
+				value = float(self)
+			else:
+				value = str(self)
+			return "{value:{spec}}".format(value=value, spec=format_spec)
 	%}
 }