Added a method for getting a user by their id (#1691)

* Added a method for getting a user by their id

* Added get_user_by_id to MainClass stubs

Fixes #1615

github/MainClass.py

@@ -275,6 +275,20 @@ class Github(object):
                 self.__requester, headers, data, completed=True
             )
 
+    def get_user_by_id(self, user_id):
+        """
+        :calls: `GET /user/:id <http://developer.github.com/v3/users>`_
+        :param user_id: int
+        :rtype: :class:`github.NamedUser.NamedUser`
+        """
+        assert isinstance(user_id, int), user_id
+        headers, data = self.__requester.requestJsonAndCheck(
+            "GET", "/user/" + str(user_id)
+        )
+        return github.NamedUser.NamedUser(
+            self.__requester, headers, data, completed=True
+        )
+
     def get_users(self, since=github.GithubObject.NotSet):
         """
         :calls: `GET /users <http://developer.github.com/v3/users>`_

github/MainClass.pyi

@@ -83,6 +83,7 @@ class Github:
     def get_user(self, login: _NotSetType = ...) -> AuthenticatedUser: ...
     @overload
     def get_user(self, login: str) -> NamedUser: ...
+    def get_user_by_id(self, user_id: int) -> NamedUser: ...
     def get_users(
         self, since: Union[int, _NotSetType] = ...
     ) -> PaginatedList[NamedUser]: ...