[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/config.py

@@ -749,7 +749,7 @@ class Config:
 
         Returns
         -------
-        Group
+        `Group <redbot.core.config.Group>`
             The guild's Group object.
 
         """
@@ -767,7 +767,7 @@ class Config:
 
         Returns
         -------
-        Group
+        `Group <redbot.core.config.Group>`
             The channel's Group object.
 
         """
@@ -783,7 +783,7 @@ class Config:
 
         Returns
         -------
-        Group
+        `Group <redbot.core.config.Group>`
             The role's Group object.
 
         """
@@ -799,7 +799,7 @@ class Config:
 
         Returns
         -------
-        Group
+        `Group <redbot.core.config.Group>`
             The user's Group object.
 
         """
@@ -815,7 +815,7 @@ class Config:
 
         Returns
         -------
-        Group
+        `Group <redbot.core.config.Group>`
             The member's Group object.
         """
         return self._get_base_group(self.MEMBER, member.guild.id, member.id)
@@ -834,7 +834,7 @@ class Config:
 
         Returns
         -------
-        Group
+        `Group <redbot.core.config.Group>`
             The custom group's Group object.
         """
         return self._get_base_group(group_identifier, *identifiers)