add ec.private_key_from_secret_and_curve (#3225)
* finish https://github.com/pyca/cryptography/pull/1973
* change API & add test
Function will now return an instance of EllipticCurvePrivateKey, as that
is the users' ultimate goal anyway.
* fix test
* improve coverage
* complete coverage
* final fix
* centos fix
* retry
* cleanup asserts
* use openssl_assert
* skip unsupported platforms
* change API name to derive_private_key
* change version added
* improve description of `secret` param
* separate successful and failure test cases
* simplify successful case
* add docs for derive_elliptic_curve_public_point
* add period
8 files changed