Function decode

decode(buffer, encoding): string
Decode the byte buffer that encoding with GBK, GB18030, GB2132, ISO8859_1 .etc to a utf-8 string.
Parameters
- buffer: any
  the byte buffer that encoding with GBK, GB18030, GB2132, ISO8859_1 .etc
- encoding: string
  the encoding method: GBK, GB18030, GB2132, ISO8859_1
Returns string
Example
```
import * as iconv from 'iconv';
import * as http from 'http';
import {Encoding} from 'buffer';

let client = http.newClient();
let resp = client.get('xxx.com/login');
let iconv.decode(resp.data, Encoding.Utf8);
```