[PROPOSE] timestamp support

This pull request is to support specifying time on the API. 

This makes possible to specify the timestamp

curl -d 'number=10&timestamp=1400068922' 'http://localhost:5125/api/a/b/c'

I wrote detailed descriptions about how to implement this feature at https://gist.github.com/sonots/3ddba0756d945c59ce5e (Japanese). This pull request implements the (1) way of it.