Updated version to 3.1.0
Added getter methods to some properties

Getters are more scalable and flexible than properties

Fixed #62
Modified comments to ensure jsduck works with them
Added Deferred.when method

To unify sync and async methods

Fixed #63
Pass action context to model by constructor

Reverted changes in
https://github.com/ecomfe/er/commit/9cd496378589a589f1042cc2de94452a9422
5f84

Fixed #66
Added method to determine whether a model has property value

Fixed #67
Added more utility methods to datasource

Fixed #68
添加mini-event的依赖
添加mini-event的依赖

增加.gitignore忽略依赖目录
Observable作为EventTarget的代理，自身不再实现

在4.0中移除`Observable`模块

Fixed #58
继承关系导至EventTarget

完全架空Observable，保证这个模块只外部必须用时用到

Fixed #58
更新mini-event版本

0.8.0存在BUG
添加alpha.1版本
更新mini-event版本
Merge pull request #72 from ecomfe/3.1.0-dev

3.1.0-alpha.1