Support tuple args in lambda

[trotterdylan]

Per justinsaccount on HN:

$ make run
c = {}
top = sorted(c.items(), key=lambda (k,v): v)
^D
Traceback (most recent call last):
File "./tools/grumpc", line 102, in
sys.exit(main(parser.parse_args()))
File "./tools/grumpc", line 60, in main
visitor.visit(mod)
File "/usr/local/Cellar/python/2.7.12/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ast.py", line 241, in visit
return visitor(node)
File "/Users/foo/src/grumpy/build/lib/python2.7/site-packages/grumpy/compiler/stmt.py", line 302, in visit_Module
self._visit_each(node.body)
File "/Users/foo/src/grumpy/build/lib/python2.7/site-packages/grumpy/compiler/stmt.py", line 632, in _visit_each
self.visit(node)
File "/usr/local/Cellar/python/2.7.12/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ast.py", line 241, in visit
return visitor(node)
File "/Users/foo/src/grumpy/build/lib/python2.7/site-packages/grumpy/compiler/stin visit_Assign
with self.expr_visitor.visit(node.value) as value:
File "/usr/local/Cellar/python/2.7.12/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ast.py", line 241, in visit
return visitor(node)
File "/Users/foo/src/grumpy/build/lib/python2.7/site-packages/grumpy/compiler/expr_visitor.py", line 101, in visit_Call
values.append((util.go_str(k.arg), self.visit(k.value)))
File "/usr/local/Cellar/python/2.7.12/Frameworks/Python.framework/Versions/2.7/lib/python2.7/ast.py", line 241, in visit
return visitor(node)
File "/Users/foo/src/grumpy/build/lib/python2.7/site-packages/grumpy/compiler/expr_visitor.py", line 246, in visit_Lambda
return self.visit_function_inline(func_node)
File "/Users/foo/src/grumpy/build/lib/python2.7/site-packages/grumpy/compiler/expr_visitor.py", line 388, in visit_function_inline
func_visitor = block.FunctionBlockVisitor(node)
File "/Users/foo/src/grumpy/build/lib/python2.7/site-packages/grumpy/compiler/block.py", line 432, in init
args = [a.id for a in node_args.args]
AttributeError: 'Tuple' object has no attribute 'id'

[JustinAzoff]

Can also reproduce it using tuple unpacking in function arguments (not very common, was removed in py3)

$ cat /tmp/foof.py
def func((a,b)):
    return b

mytuple = 1,2
print func(mytuple)
$ python /tmp/foof.py
2