Support syntax for variable annotation in Python 3.6

[east825]

PEP 526 introduced the syntax for variable annotations in Python 3.6. At the moment pycodestyle.py warns of every such annotation taking them for "E701 multiple statements on one line (colon)":

from typing import ClassVar, List

CONST: int = 42  # E701


class Class:
    cls_var: ClassVar[str]  # E701

    def m(self):
        xs: List[int] = []  # E701

$ python3.6 pycodestyle.py variable_annotations.py 
variable_annotations.py:3:6: E701 multiple statements on one line (colon)
variable_annotations.py:7:12: E701 multiple statements on one line (colon)
variable_annotations.py:10:11: E701 multiple statements on one line (colon)

[hassanselim0]

The following doesn't work as expected:

class Person:
    name: str

Pycodestyle returns 'name' used before definition