wolfSSL's source tree had a stale version of the Python wolfCrypt
wrapper. There were a couple of bits in it that weren't here, so this
ports them accross.
Mostly notably a minor issue where `Random.__del__` can throw a race
condition exception during shutdown.
* Fix some path and compiler things for Windows
* Move source code to align better with Python standards
* Have setup.py build wolfSSL and FFI
* Update Python versions in tox
* Add CMake building for Windows build
* Add missing __init__.py for tox
* Make wolfSSL a git submodule
Andrew Hutchings
Moisés Guimarães