fix README
script rename
refactor error_handle's unittest
translate document of extend_json to English
refactor extend_json's unittest
small fix
fix document error, arrange document
rename _CantEncodeObjException to CantEncodeObjException

because encoders from outside may use it too.
improve unittest
translate some document to English
fix document
安全起见 predicates 只允许返回 bool 值或 dict(value=new_value)

要不然，用户创建 trans 类型的 predicates 时，可能会下意识的直接返回新值，忘了使用 dict(value=new_value)
格式。结果这个返回值会被转换为布尔值拿去进行合法性判断，而字段值则没有被更新。
fix doc error
修正 PopulatorArgument 使其支持最新的 flask_restful
refactor test of model extend
translate comments
rename test/ to tests/
file rename
changes default callback_name_source from 'jsonp' to 'callback'

because jQuery default use 'callback'
update doc