Support mypy annotations using comment syntax

This allows us to use mypy annotations for completion in Python 2.

Closes #946

test/completion/pep0484_comments.py

@@ -47,7 +47,7 @@ b
 class Employee:
     pass
 
-from typing import List
+from typing import List, Tuple
 x = []   # type: List[Employee]
 #? Employee()
 x[1]
@@ -103,3 +103,67 @@ aaa = some_extremely_long_function_name_that_doesnt_leave_room_for_hints() \
     # type: float # We should be able to put hints on the next line with a \
 #? float()
 aaa
+
+# Test instance methods
+class Dog:
+    def __init__(self, age, friends, name):
+        # type: (int, List[Tuple[str, Dog]], str) -> None
+        #? int()
+        self.age = age
+        self.friends = friends
+
+        #? Dog()
+        friends[0][1]
+
+        #? str()
+        self.name = name
+
+    def friend_for_name(self, name):
+        # type: (str) -> Dog
+        for (friend_name, friend) in self.friends:
+            if friend_name == name:
+                return friend
+        raise ValueError()
+
+    def bark(self):
+        pass
+
+buddy = Dog(UNKNOWN_NAME1, UNKNOWN_NAME2, UNKNOWN_NAME3)
+friend = buddy.friend_for_name('buster')
+# type of friend is determined by function return type
+#! 9 ['def bark']
+friend.bark()
+
+friend = buddy.friends[0][1]
+# type of friend is determined by function parameter type
+#! 9 ['def bark']
+friend.bark()
+
+# type is determined by function parameter type following nested generics
+#? str()
+friend.name
+
+# Mypy comment describing function return type.
+def annot():
+    # type: () -> str
+    pass
+
+#? str()
+annot()
+
+# Mypy variable type annotation.
+x = UNKNOWN_NAME2  # type: str
+
+#? str()
+x
+
+class Cat(object):
+    def __init__(self, age, friends, name):
+        # type: (int, List[Dog], str) -> None
+        self.age = age
+        self.friends = friends
+        self.name = name
+
+cat = Cat(UNKNOWN_NAME4, UNKNOWN_NAME5, UNKNOWN_NAME6)
+#? str()
+cat.name