Add new features from new layer (#3676)

Updated some documentation regarding raw API.
get_permissions has been adjusted.
Expose more parameters when sending messages.
Update chat action.
Support sending spoilers.
Update buttons.

telethon/_misc/markdown.py

@@ -19,6 +19,7 @@ DELIMITERS = {
     _tl.MessageEntityCode: ('`', '`'),
     _tl.MessageEntityItalic: ('_', '_'),
     _tl.MessageEntityStrike: ('~~', '~~'),
+    _tl.MessageEntitySpoiler: ('||', '||'),
     _tl.MessageEntityUnderline: ('# ', ''),
 }