ENH: support python 3

* closes #56
* running `2to3 rdtools/` shows the only incompatibilities are the
 relative imports already addressed in #67 so merge #68 to fix imports
* running `2to3 tests/` shows python 2 print commands, so rerun 2to3
with `-f print -w -n` to add parentheses to print statements to make
them calls instead of commands, altho these should really be replaced
by logging, so TODO: make another issue and PR to add logging to tests

Signed-off-by: Mark Mikofski <bwana.marko@yahoo.com>

tests/degradation_test.py

@@ -108,43 +108,43 @@ def test_degradation_with_ols(cls):
         ''' Test degradation with ols. '''
 
         funcName = sys._getframe().f_code.co_name
-        print '\r', 'Running ', funcName
+        print('\r', 'Running ', funcName)
 
         # test ols degradation calc
         for input_freq in cls.list_ols_input_freq:
-            print 'Frequency: ', input_freq
+            print('Frequency: ', input_freq)
             rd_result = degradation_ols(cls.test_corr_energy[input_freq])
             cls.assertAlmostEqual(rd_result[0], 100 * cls.rd, places=1)
-            print 'Actual: ', 100 * cls.rd
-            print 'Estimated: ', rd_result[0]
+            print('Actual: ', 100 * cls.rd)
+            print('Estimated: ', rd_result[0])
 
     def test_degradation_classical_decomposition(cls):
         ''' Test degradation with classical decomposition. '''
 
         funcName = sys._getframe().f_code.co_name
-        print '\r', 'Running ', funcName
+        print('\r', 'Running ', funcName)
 
         # test classical decomposition degradation calc
         for input_freq in cls.list_CD_input_freq:
-            print 'Frequency: ', input_freq
+            print('Frequency: ', input_freq)
             rd_result = degradation_classical_decomposition(cls.test_corr_energy[input_freq])
             cls.assertAlmostEqual(rd_result[0], 100 * cls.rd, places=1)
-            print 'Actual: ', 100 * cls.rd
-            print 'Estimated: ', rd_result[0]
+            print('Actual: ', 100 * cls.rd)
+            print('Estimated: ', rd_result[0])
 
     def test_degradation_year_on_year(cls):
         ''' Test degradation with year on year approach. '''
 
         funcName = sys._getframe().f_code.co_name
-        print '\r', 'Running ', funcName
+        print('\r', 'Running ', funcName)
 
         # test YOY degradation calc
         for input_freq in cls.list_YOY_input_freq:
-            print 'Frequency: ', input_freq
+            print('Frequency: ', input_freq)
             rd_result = degradation_year_on_year(cls.test_corr_energy[input_freq])
             cls.assertAlmostEqual(rd_result[0], 100 * cls.rd, places=1)
-            print 'Actual: ', 100 * cls.rd
-            print 'Estimated: ', rd_result[0]
+            print('Actual: ', 100 * cls.rd)
+            print('Estimated: ', rd_result[0])
 
 if __name__ == '__main__':
     unittest.main()