* switch to xdist in tox for faster runs

* not using auto to avoid too many processes on local laptops
* we need to use pytest-cov to generate coverage properly now

* these env vars aren't present on no coverage builds

* tox changes

* we already do this check in other places

This test is *incredibly* expensive and we already do roundtrips like
this on other DH groups. To make this test less expensive and also more
accurate to its name we now verify that the parameters on the generated
key match

* empty commit

the most important CI feature

* subtests ec

* continue instead of return

* indentation

* remove AES tests we will always skip

* constrain <64-bit IV vector removal to just GCM

* apparently this is only used by GCM

* Drop Python 2

* Black everything