sp_chunk and sp_chunkref implemented

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
CT_ASSERT (compile-time assert) macro added

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
Implementation of sp_msg with separate header and body

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>
sending messages uses zero-copy now

Signed-off-by: Martin Sustrik <sustrik@250bpm.com>