added callbacks to repack_bits, stream_to_tagged_stream and stream_mux in gr-blocks, added callback to packet_headergenerator in gr-digital, added new constellations objects to gr-digital, added smoother to throttle to decrease delay, corrected the trellis_encoder's callback function, corrected chunks_to_symbols' callback function set_symbol_table

Hi all,

I added callback functions to both bits per input and output bytes of repack_bits in gr-blocks to make it able to be changed dynamically. 
Similarly, I added callback functions to stream_to_tagged_stream and stream_mux to enable dynamical change of parameters.
I also added callback function set_header to packet_headergenerator to  make the header able to be chaned dynamically.

I've also added two constellations objects in the constellation of gr-digital. One of the constellation object is the natural mapped 8psk and the other is a 16qam. These two constellations are both used in trellis coded modulations based on the paper by G. Ungerboeck "Channel coding with multilevel/phase signals", IEEE Trans. Info Theory, vol. IT-28, pp. 55–67, 1982. 

I found the trellis_encoder.grc missed the callback function set_K, so I added it to make it work. 

I found the chunks_to_symbols has callback function set_symbol_table, but it wasn't working! I found it missed the set_symbol_table in chunks_to_symbols.grc and chunks_to_symbols.h, and added const to std::vector<@O_TYPE> &symbol_table to make it work.

@anastas found there exists huge delay in a system we are working on due to some buffer in the queue. He modified the throttle to decrease the delay by decreasing the samples throttle process at a time. 
So the throttle was modified by adding an optional parameter max_noutput_items.

Could you check the changes and merge them to the gnuradio if possible. 

Thanks!
Best,
Zhe