Changes in this release:
* Fix bugs with string handling for information coming from library, slot and token
* Add certificate, key and signature interchange functions for X.509 and OpenSSL
* Fix bugs/add tests when exchanging data with OpenSSL/Python crypto libraries
* Cache object properties
* Fix encoding of EC_POINT for `derive_key`
* Use `AES_MAC` as the default signing/verification mechanism for AES
* Fix some crashes, e.g. when no mechanisms are present