Better documentation

[kcwu]

Please provide better documentation.
Explain the rule syntax and each codecs

[buganini]

@Artoria2e5 I have some document in gh-pages branch
http://buganini.github.io/bsdconv/
this is generated from https://github.com/buganini/bsdconv/tree/master/doc

And http://www.slideshare.net/Buganini/bsdconv
generated from https://github.com/buganini/bsdconv/tree/master/doc/tex

Since github wiki is yet another repo (not so good for archiving) so I prefer to stick with gh-pages, but it's still fine if you'd like to use wiki.