Add __iter__ function to Args object

[nathancahill]

Currently, looping over arguments.Args() returns None infinitely. This adds support for iterating over Args

Currently:

>>> for arg in arguments.Args():
>>>    print arg
None
None
...
None

With __iter__:

>>> for arg in arguments.Args():
>>>    print arg
arg1
arg2

[wkentaro]

+1