Support declaring function signature in a comment

[JukkaL]

Make it possible to declare function signature in a comment. This makes is possible to write statically typed code that is valid Python 2. Here is a trivial example:

def inc(x):
    # type: (int) -> int
    return x + 1

Also let the type comment included on the same line as the function header:

def inc(x): # type: (int) -> int
    return x + 1

Methods should not include a type for the self argument:

class A:
    def foo(self, x, y): # type: (int, str) -> None
        pass

Note that this is not good for writing overloaded functions. An alternative syntax, such as using a function decorator, is needed for this (in a separate issue).

[JukkaL]

For *args and **kwargs there should be a corresponding * or ** in the signature:

def foo(x, *y): # type: (int, *str) -> None
    ...
def bar(x, **y): # type: (int, **bool) -> None
    ...

Arguments with default values don't need anything special:

def foo(x, y=1): # type: (int, int) -> None
    passs