Add SayAlphaCase and similar functionality for AGI

This adds a new dialplan application, SayAlphaCase, that performs much
the same function as SayAlpha except that it takes additional options
which allow the user to specify whether the case of each letter should
be announced for uppercase, lowercase, or all letters. Similar
functionality has been added to the SAY ALPHA AGI command via an
optional parameter.

Original Patch by: Kevin Scott Adams
Reported by: Kevin Scott Adams
Review: https://reviewboard.asterisk.org/r/2725/
(closes issue ASTERISK-20782)


git-svn-id: http://svn.asterisk.org/svn/asterisk/trunk@397493 f38db490-d61c-443f-a65b-d21fe96a405b