optimisation of 8-16kHz funcs

git-svn-id: https://svn.code.sf.net/p/freetel/code/codec2-dev@1812 01035d8c-6547-0410-b346-abe4f91aad63
FreeDV tx & rx working in real time.  Yayyyyyyyyy

git-svn-id: https://svn.code.sf.net/p/freetel/code/codec2-dev@1813 01035d8c-6547-0410-b346-abe4f91aad63