blocks:added smoother to throttle to decrease delay

throttle modification
digital: fixied the bug in chunks_to_symbols that the callback function set_symbol_table doesn't work

digital: kept the original code for setting the symbol_table for chunks_to_symbols
digital: added callback function set_header_formatter to packet_headergenerator_bb
digital:added new constellations objects naturally mapped 8PSK and 16QAM

cleaned constellation
trellis: corrected a missing callback function set_K in trellis_encoder
blocks: added callback functions to stream_mux and stream_to_tagged_stream

perfected stream_mux and stream_to_tagged_stream

perfected stream_mux_impl.h