Add the procedure to generate a SSL context.
Add the procedure to generate a SSL context.

* The implementation is largely based on ssl.create_default_context()
  (with some security enhancement).
* I think TLSv1.0 should be disabled as well, but the problem is that
  TLSv1.1/1.2 is suported natively only in Python 3.4 or later. Should
  we kill Python 3.3 support for the sake of better security?

fujimotos/Eubin