DDSSEC13 — Add support for ChaCha20

The AES-CCM cypher suite used by the built-in authentication plugins is well suited for higher end processors that have hardware support for AES (e.g. the Intel AES-NI instructions and the the AES instructions in ARMv8).

ARMv7 and other low-end processors don't have hardware support. In these AES can be quite slow.

To better support lower end processors it would be good to add support for a cypher suite that has reasonable performance without hardware support. The industry seems to be converging around the ChaCha20. See:

https://tools.ietf.org/html/rfc8439
https://tools.ietf.org/html/rfc7905

Gerardo