Merge pull request #52 from lianqin7/master

fixed #43 required & rule bug
U: improve docs
U: remove unnecessary code
U: improve docs
U: improve docs
U: improve examples
U: fix docs error
Update api.md

修改Core#excuete的描述，更加详细
Merge pull request #57 from luffyfly/patch-1

Update api.md
U: rebuild
Merge pull request #2 from aralejs/master

merge master