Ruby Grape,sinatra下的自动加载代码

 实现rack应用加载的几种方法：

Reload feature in development environment

[gem guard-rack] http://code.dblock.org/2012/02/23/watching-rack-application-changes-with-guard-rack.html
run: bundle exec guard #eg. grape-on-rack

[gem shot-gun] https://github.com/rtomayko/shotgun

[gem rerun] https://github.com/alexch/rerun