Add SayPhonetic and SayAlpha applications (bug #793)

Makefile

apps/app_agi.c

asterisk.c

configs/logger.conf.sample

include/asterisk/say.h

pbx.c

say.c

sounds.txt

sounds/letters/a.gsm

sounds/letters/at.gsm

sounds/letters/b.gsm

sounds/letters/c.gsm

sounds/letters/d.gsm

sounds/letters/dash.gsm

sounds/letters/dollar.gsm

sounds/letters/dot.gsm

sounds/letters/e.gsm

sounds/letters/equals.gsm

sounds/letters/exclaimation-point.gsm

sounds/letters/f.gsm