sntrup4591761x25519-sha512@tinyssh.org using the Streamlined NTRU Prime
4591^761 implementation from SUPERCOP coupled with X25519 as a stop-loss. Not
enabled by default.
introduce KEM API; a simplified framework for DH-ish KEX methods.
from markus@ feedback & ok djm@
OpenBSD-Commit-ID: d687f76cffd3561dd73eb302d17a1c3bf321d1a7