Support declarations of cpp inplace operators like '+='

Cython/Compiler/Parsing.py

@@ -2875,6 +2875,7 @@ supported_overloaded_operators = cython.declare(set, set([
     '++', '--', '~', '|', '&', '^', '<<', '>>', ',',
     '==', '!=', '>=', '>', '<=', '<',
     '[]', '()', '!', '=',
+    '+=', '-=', '*=', '/=', '%=', '|=', '&=', '<<=', '>>=',
     'bool',
 ]))