[MOD] Make vcard-avatars XEP-0421 tier

README.MD

@@ -42,6 +42,8 @@ TODO
     we _might_ just manage to get some system that can at least emulate that, 
     and hopefully be reasonably faster than the filesystem, with some added 
     reliability.
+        - You can always concat paths, and search by prefix with LMDB. ~512 bytes 
+        a key is more than enough. I'll just need to write a good abstraction layer.
 - Get rid of the '?'-syntax and use another invalid Matrix char/valid XMPP char 
 ('$'?) for escaped