Merge pull request #19 from atian25/master

2个严重bug和一个特性
Merge pull request #20 from atian25/master

mapping也可以是function
Merge pull request #21 from atian25/master

little fixed
fix minor err
Merge pull request #22 from JacksonTian/bugfix

fix minor err
Merge branch 'master' of github.com:ktmud/weixin-robot
提取出签名计算

Signed-off-by: TZ <atian25@qq.com>