Added ability to upload and send media, and more fixes

Uploading and sending media are different things.
Once you have uploaded a media file, you can send
it to many users without uploading it again, since
you have a handle to the uploaded file.

Other fixes include not showing additional data
on error messages and not generating correct
code for sending bytes

errors.py

@@ -163,10 +163,11 @@ class RPCError(Exception):
                 # Get additional_data, if any
                 if match.groups():
                     self.additional_data = int(match.group(1))
+                    super().__init__(self, error_msg.format(self.additional_data))
                 else:
                     self.additional_data = None
+                    super().__init__(self, error_msg)
 
-                super().__init__(self, error_msg)
                 called_super = True
                 break