apply zz_<libname>_ prefix to all linker-visible objects on the C side

- buffer -> zz_buffer
- cmp_buffer_state -> zz_cmp_buffer_state
- cmp_buffer_reader -> zz_cmp_buffer_reader
- cmp_buffer_writer -> zz_cmp_buffer_writer
- zzlua_Stat* -> zz_file_Stat*
- zz_stat -> zz_file_stat
- zz_lstat -> zz_file_lstat
- zz_dirent_name -> zz_file_dirent_name
- ZZ_PORTS_MAX -> ZZ_JACK_PORTS_MAX

the rule for globals:

- zzlua_run -> zz_run
- setup_signal_handler_thread -> zz_setup_signal_handler_thread
no need to remove cmp.o upon 'make clean'
change dynamic parameter of zz_buffer_t from bool to int
move cmp-zz_buffer interop to msgpack