added -8-16 kHz sample rate conversion with shorts used for 16 kHz side

git-svn-id: https://svn.code.sf.net/p/freetel/code/codec2-dev@1809 01035d8c-6547-0410-b346-abe4f91aad63
made both args shorts for 8-16 kHz sample rate conversion

git-svn-id: https://svn.code.sf.net/p/freetel/code/codec2-dev@1810 01035d8c-6547-0410-b346-abe4f91aad63