update gen_big5.pl

1. update reference URL
2. add comment header at output file
update 5c5c.pl: add main() and message
remove chn-2.pl: useless now
rename chn-3.pl to big5-text-io-demo.pl
move big5.txt to data folder
update big5-text-io-demo.pl

add message
update lib and data file path
update big5.txt: add comment header

This data file is generated by gen_big5.pl
There are several script need it for reference table.
update encoding-tw for more message