Change the build/publish process and add example

• Use pre-built Javascript instead of post-built Javascript;
• Add example about how the library is supposed to be used.

Fix fclose(NULL) bug

Fixed a bug when the nodejs' garbage collector runs.

Refactor many things

• use <cstdio> for file buffering;
• use iconv-lite as an internal encoding converter;
• this project now has an api reference page;