TODO List Functionality

[brdoney]

It would be nice to have some TODO list functionality within the bot, so lists could be created and checked off as needed. The user interactions could be similar to the following:

1. List lists

   $ -todo
   **Created Lists:**
   * List A
   * List B
   * List C
   

2. Create list

   $ -todo -c <list_name>
   Created list <list_name>
   

3. Delete the entire list

   $ -todo -d <list_name>
   Deleted list <list_name>
   

4. Display list

   -todo <list_name>
   **List <list_name>:**
   [_] Incomplete item
   [✓] Complete item
   

5. Add things to list

   $ -todo <list_name> -a <string to add>
   **List <list_name>:**
   [_] Incomplete item
   [✓] Complete item
   [_] <string to add>
   

6. Check off things

    $ -todo <list_name> -c <number_to_check_off>
   

7. Uncheck things

   $ -todo <list_name> -u <number_to_check_off>