All charsets can be auto-generated from external source now

Now here is approx how it works:
- generate.sh fetches external maps from unicode.org and o'reilly mirror
- gen-charset.pl parses them one by one and spits out generated C sources

Some special notes:
- Big5hkscs file untouched, I still haven't decided to improve it or drop it altogether
- Big5 is now using CP950 as source instead of Adobe cmap.
- Windows Latin1 is now using CP1252 (I assume this is the original intention)
- The scripts won't be dist'ed since it's maintainer's job to refresh the encodings and dist the generated sources instead