Begin work on a data request API (#4045)

[Core] Data Deletion And Disclosure APIs

 - Adds a Data Deletion API
   - Deletion comes in a few forms based on who is requesting
   - Deletion must be handled by 3rd party
 - Adds a Data Collection Disclosure Command
   - Provides a dynamically generated statement from 3rd party
   extensions
 - Modifies the always available commands to be cog compatible
   - Also prevents them from being unloaded accidentally

docs/guide_cog_creation.rst

@@ -98,6 +98,7 @@ Open :code:`__init__.py`. In that file, place the following:
 
     from .mycog import Mycog
 
+
     def setup(bot):
         bot.add_cog(Mycog())
 
@@ -238,3 +239,20 @@ Not all of these are strict requirements (some are) but are all generally advisa
     but a cog which takes actions based on messages should not.
 
 15. Respect settings when treating non command messages as commands.
+
+16. Handle user data responsibly
+
+  - Don't do unexpected things with user data.
+  - Don't expose user data to additional audiences without permission.
+  - Don't collect data your cogs don't need.
+  - Don't store data in unexpected locations.
+    Utilize the cog data path, Config, or if you need something more
+    prompt the owner to provide it.
+
+17. Utilize the data deletion and statement APIs
+
+  - See `redbot.core.commands.Cog.red_delete_data_for_user`
+  - Make a statement about what data your cogs use with the module level
+    variable ``__red_end_user_data_statement__``.
+    This should be a string containing a user friendly explanation of what data
+    your cog stores and why.