支持 Mock.mock( rurl, [rtype], function( options ) ) 的回调函数返回 Promise 对象

[luozhihua]

支持以下 mock 方式：

Mock.mock(/.json/, 'post', function() {
    return new Promise(function(resolve, reject) {
        setTimeout(function() {
            resolve(Mock.mock({
                name: "@cname"
            }))
        })
    })
})

[coveralls]

Changes Unknown when pulling 53e0d21 on luozhihua:refactoring into ** on nuysoft:refactoring**.

[coveralls]

Changes Unknown when pulling d6ae91f on luozhihua:refactoring into ** on nuysoft:refactoring**.