The subject can be an empty string

When cert errors where detected the certificate-set signal did overwrite
the certficition errors which were already modified by accept_certificate()

This simplifies the code and removes the certificate-set signal

Previously we passed the timeout to send_stanza() which would not
allow to set timeouts on other non-stanza related tasks.

Issue a disconnected signal on any zero data read

Instead of enforcing stringprep or precis, try stringprep and fallback
to precis otherwise.

This makes `python -m nbxmpp.examples.client` work

NOTES: You can set the env variable NBXMPP_USE_PRECIS to revert back
to the old behavior.

Philipp Hörist authored Aug 28, 2022 and Philipp Hörist committed Aug 28, 2022

- Move sending stanzas out of mechanism impl
- Add missing SHA-512-PLUS method
- Add type hints

The default timeout seems to be 60 seconds which is much too long.

Fixes #130