Add support for async for. Issue #124

Ignore 'boilerplate' opcodes that set up the async iteration logic internally (https://www.python.org/dev/peps/pep-0492/#asynchronous-iterators-and-async-for) - We don’t need any of this as GET_AITER is enough to tell us that we are in an `async for`.

tests/input/async_for.py

@@ -0,0 +1,44 @@
+async def a(b, c):
+    async for b in c:
+        pass
+
+async def a(b, c):
+    async for b in c:
+        continue
+
+async def a(b, c):
+    async for b in c:
+        break
+
+async def time_for_some_fun():
+    async for (x, y) in myfunc(c):
+        print(123)
+        if (x == 3):
+            print('something')
+            break
+
+        for i in regular_for:
+            var1 = var2 + var3
+            async for x1 in print:
+                print('test LOAD_GLOBAL')
+                async for x2 in inner:
+                    for x3 in regular:
+                        async for x4 in inner2:
+                            async for x5 in inner3:
+                                async for x6 in inner4:
+                                    print('ridiculous nesting')
+
+    async for (q, w, e, r) in qwer:
+        u = 1 + 2 + 3
+
+    async for x4 in inner2:
+        async for x5 in inner3:
+            pass
+        
+    print('outside loop')
+
+print ('outside function')
+
+# The following will LOAD_METHOD, not GET_AITER or GET_ANEXT.
+# test.__anext__(iter)
+# test.__aiter__(iter)

tests/tokenized/async_for.txt

@@ -0,0 +1,70 @@
+async def a ( b , c ) : <EOL>
+<INDENT>
+async for b in c : <EOL>
+<INDENT>
+pass <EOL>
+<OUTDENT>
+<OUTDENT>
+async def a ( b , c ) : <EOL>
+<INDENT>
+async for b in c : <EOL>
+<INDENT>
+continue <EOL>
+<OUTDENT>
+<OUTDENT>
+async def a ( b , c ) : <EOL>
+<INDENT>
+async for b in c : <EOL>
+<INDENT>
+break <EOL>
+<OUTDENT>
+<OUTDENT>
+async def time_for_some_fun ( ) : <EOL>
+<INDENT>
+async for x , y in myfunc ( c ) : <EOL>
+<INDENT>
+print ( 123 ) <EOL>
+if x == 3 : <EOL>
+<INDENT>
+print ( 'something' ) <EOL>
+break <EOL>
+<OUTDENT>
+for i in regular_for : <EOL>
+<INDENT>
+var1 = var2 + var3 <EOL>
+async for x1 in print : <EOL>
+<INDENT>
+print ( 'test LOAD_GLOBAL' ) <EOL>
+async for x2 in inner : <EOL>
+<INDENT>
+for x3 in regular : <EOL>
+<INDENT>
+async for x4 in inner2 : <EOL>
+<INDENT>
+async for x5 in inner3 : <EOL>
+<INDENT>
+async for x6 in inner4 : <EOL>
+<INDENT>
+print ( 'ridiculous nesting' ) <EOL>
+<OUTDENT>
+<OUTDENT>
+<OUTDENT>
+<OUTDENT>
+<OUTDENT>
+<OUTDENT>
+<OUTDENT>
+<OUTDENT>
+async for q , w , e , r in qwer : <EOL>
+<INDENT>
+u = 6 <EOL>
+<OUTDENT>
+async for x4 in inner2 : <EOL>
+<INDENT>
+async for x5 in inner3 : <EOL>
+<INDENT>
+pass <EOL>
+<OUTDENT>
+<OUTDENT>
+print ( 'outside loop' ) <EOL>
+<OUTDENT>
+print ( 'outside function' ) <EOL>