Remove u'' prefix and L suffix which do not appear under Python 3

Author: keszybz

igor/struct.py

@@ -429,7 +429,7 @@ class Structure (_struct.Struct):
                'time': 303240213}],
      'version': 1}
     >>> [hex(x) for x in d['runs'][0]['data'].flat]
-    ['0x607L', '0x809L', '0xa0bL', '0xc0dL', '0xe0fL', '0x1011L']
+    ['0x607', '0x809', '0xa0b', '0xc0d', '0xe0f', '0x1011']
 
     You can also read out from strings:
 

test/test-igorpy.py

@@ -75,9 +75,9 @@
         ...
         0.00077303,  0.00038651,  0.        ]), array([], dtype=float64), array([], dtype=float64), array([], dtype=float64)]
 >>> d.W_plrX5.data_units
-(u'', '', '', '')
+('', '', '', '')
 >>> d.W_plrX5.axis_units
-(u'', '', '', '')
+('', '', '', '')
 >>> d.W_plrX5.data  # doctest: +ELLIPSIS
 array([  1.83690956e-17,   2.69450769e-02,   7.65399113e-02,
          1.44305170e-01,   2.23293692e-01,   3.04783821e-01,