This puts a new minimum on the PEP 518 requirement for `setuptools`
because older versions of setuptools' PEP 517 backend will fail to
include `setup.py` in an sdist.
* allow bytearrays for key/iv for symmetric encryption
* bump pypy/cffi requirements
* update docs, fix some tests
* old openssl is naught but pain
* revert a typo
* use trusty for old pypy
* better error msg again
* restore match
