[V3 Docs] Remove all build warnings (#1640)

* Upgrade sphinx version to 1.7+

* Fix title overlines/underlines in autostart_systemd.rst

* Skip trying to document a method from discord.py

* Add escaped space after backtick

* Escape underscores (sphinx tries to interpret a hyperlink)

* Use fully qualified reference for class

* Fix reference in tunnel.py

* Remove python syntax highlighting in data_converter.py

For some reason sphinx couldn't lex these as python. Removing the highlighting seems like the logical solution for now, since if it wasn't being lexed, it wouldn't highlight anyway.

* Comment out static path since we're not using it right now

* Update sphinx version in docs requirements too

Would rather remove this duplication but RTD is a special snowflake

redbot/core/utils/tunnel.py

@@ -112,13 +112,13 @@ class Tunnel(metaclass=TunnelMeta):
             The message content
         embed: `discord.Embed`
             The embed to send
-        files: `List[discord.Files]`
+        files: `list` of `discord.File`
             A list of files to send.
-        
+
         Returns
         -------
         list of `discord.Message`
-            The `discord.Message`(s) sent as a result
+            The `discord.Message`\ (s) sent as a result
 
         Raises
         ------