New port: net/mod_amd

Asterisk app_amd for FreeSWITCH

This is an implementation of Asterisk's answering machine detection
(voice activity detection) for FreeSWITCH.

WWW: https://github.com/seanbright/mod_amd

PR: 211773
Submitted by: Šimun Mikecin <numisemis@yahoo.com>
Reviewed by: koobs