Add :++, :-- and :** to Macro#binary_op_props

This is about Issue #1865.

Thank you for the reference to elixir_parser.yrl. I've included the :++, :-- and :**  in the table. I am leaving the other ones (the followings), as I could find specific error cases.

- :->  
    - "fn -> xxx end" seems working fine.
- :~~~
    - It seems like unary operator though it's in binary_ops macro.
- :,
    - The list representation [1,2,3] is working fine.