Instead just decode stuff at the call-sites -- 100% of which were passing bytes

They are a noop on 1.1.0+ and pyOpenSSL only supports 1.1.0+ now due to
cryptography versions

* Expose DTLS_METHOD and friends

* Expose OP_NO_RENEGOTIATION

* Expose DTLS MTU-related functions

* Expose DTLSv1_listen and associated callbacks

* Add a basic DTLS test

* Cope with old versions of openssl/libressl

* blacken

* Soothe flake8

* Add temporary hack to skip DTLS test on old cryptography versions

* Update for cryptography v35 release

* Add changelog entry

* Fix versionadded::

* get_cleartext_mtu doesn't exist on decrepit old openssl

* Rewrite DTLS test to work around stupid OpenSSL misbehavior

* flake8 go away

* minor tidying

* Check for invalid ALPN lists before calling OpenSSL, for consistency

Fixes gh-1043

* Soothe flake8

* py27 going, going, gone

* black

* more black

* ok then

* forgot to remove pypy2

* add Context.set_*_proto_version, fix #860

* docs: add new openssl tls methods

* accept the fact that nothing can be taken for granted

* bump minimum required cryptography version to 3.3

* drop support for Python 3.5

* use binary wheels for cryptography

* Revert "use binary wheels for cryptography"

This reverts commit 91a04c612ed1d0dd9fd541dfefe21cac7c25b1c1.

* docker ci: compile cryptography with rust