replace double-slash comments with old-skool slash asterisk ones;
define uint16_t etc for Windows ourselves and remove ms_stdint.h &
stdint_msvc.h as no longer used;
(backend (excepting test suite) now C89 compatible)
LICENSE: move from backend to root and move COPYING to frontend, with
copies in frontend_qt & backend_qt, so in where it applies;
add LICENSE section from manual to root README