BREAKING CHANGE: getting decoded gbk post data has changed.
Before:
import {post} from 'api/HTTP';
post('http://foo.bar', {header: {}, body: 'foo'});
After:
import {bgkFetch} from 'api/HTTP';
gbkFetch('POST', 'http://foo.bar', {header: {}, body: 'foo'});
Since fetching data and decoding them from gbk by GET or POST method is barely the same, it's no need to make them two functions.