Add support for PKCS#11 libraries

[joernheissler]

PKCS#11 libraries could be supported, e.g through cffi.
There might already be such a python wrapper.

This is not the preferred way; a pure python implementation should be written for each device. Even if it means lots of work and lots of unsupported devices.
Hopefully one day all vendors will provide detailed documentation.
They earn their money with selling certified hardware, not with selling proprietary support libraries.