consolidate API functions for saying numbers/digits/alpha/phonetic into less...

consolidate API functions for saying numbers/digits/alpha/phonetic into less functions, using more efficient and clearer code (inspired by bug #4414)


git-svn-id: https://origsvn.digium.com/svn/asterisk/trunk@5819 65c4cc65-6c06-0410-ace0-fbb531ad65f3