koajs/koa — pull request #227 by dead-horse (2014-02-26 17:54:04+00:00)
Title: make res.charset also work before res.type

provide more friendly usage for res.charset
not longer need to put res.charset after res.type

```
res.charset = 'gbk';
res.type = 'text/html';

res.charset = 'gbk';
res.body = '';

res.charset = 'gbk';
res.body = {foo: 'bar'}
```