* TLS module major overhaul

* Clean TLS directory

* TLS 1.3 packets and basic client automaton (+ session fixes)

* Fix multiple key share entries

* Convergence py3

* Support features from cryptography v2.0

* Validate CertificateVerify signatures

* Small fix on TLS signature parsing

* Small fixes in TLS module

* Enhance Encrypted PMS support

* Convergence py3 - print

* Revert useless changes

* Strengthen crypto lib validation

Pypy won't run crypto tests on Travis CI because the cryptography
module cannot be installed with the Pypy version used.

cert.py improvements

* Improve cert.py : independence from openssl, ECDSA support, sign/verify capabilities

* Make travis install python-ecdsa

* Clarify ECDSA support

* Cleaning up for cert.py