Modernize code to use f-strings

This also removes the encoding on the top, since Python 3 does it by
default. It also changes some methods to use `yield from`.

discord/audit_logs.py

@@ -1,5 +1,3 @@
-# -*- coding: utf-8 -*-
-
 """
 The MIT License (MIT)
 
@@ -94,7 +92,7 @@ class AuditLogDiff:
 
     def __repr__(self):
         values = ' '.join('%s=%r' % item for item in self.__dict__.items())
-        return '<AuditLogDiff %s>' % values
+        return f'<AuditLogDiff {values}>'
 
 class AuditLogChanges:
     TRANSFORMERS = {
@@ -166,7 +164,7 @@ class AuditLogChanges:
             self.before.color = self.before.colour
 
     def __repr__(self):
-        return '<AuditLogChanges before=%r after=%r>' % (self.before, self.after)
+        return f'<AuditLogChanges before={self.before!r} after={self.after!r}>'
 
     def _handle_role(self, first, second, entry, elem):
         if not hasattr(first, 'roles'):