Switched everything to use cryptography instead of pyCrypto

Motivation:

* Adds PyPy support
* Performance improvement
* OpenSSL and friends are better audited than PyCrypto
* Easier windows install flow (Cryptography provides statically linked wheels
  on Windows)

This PR is basically complete on the code side, of course it can always use
more review :-)

Tests all pass locally (tested with PyPy!)

Still needs some docs work, and to figure out how to do this with the version
numbers so people's stuff doesn't suddenly get broken.
I absolutely think that as maintainers of distro packages update Parmaiko
they'll package cryptography, if it isn't already available, and we'll work
with those maintainers. (We're also in FreeBSD, adn some other weird
distros :-) and work closely with those upstream maintainers).

On Thu, Sep 18, 2014 at 6:19 PM, Jeff Forcier <notifications@github.com>
wrote:

> In sites/www/installing.rst:
>
> >
> >  C extension
> >  -----------
> >
> > -Unless you are installing from a precompiled source such as a Debian apt
> > -repository or RedHat RPM, or using :ref:`pypm <pypm>`, you will also need the
> > -ability to build Python C-based modules from source in order to install
> > -PyCrypto. Users on **Unix-based platforms** such as Ubuntu or Mac OS X will
>
> Well, Paramiko is presently packaged on a number of distros (who also
> usually package PyCrypto) and I'd expect this to continue, even if it means
> maintainers need to start packaging Cryptography too. Either way I think
> the note is useful for some newbies and doesn't harm anything by existing.
>
> —
> Reply to this email directly or view it on GitHub
> <https://github.com/paramiko/paramiko/pull/394/files#r17765412>.
>



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