add ruby/ngx_mruby framework

Hello,

I was able to get this installed and running in a vagrant dev env.
It does exit after running the test, so there may be a bug in my code or the current suite.

Any pointers would be appreciated.

thanks
@kbrock Should we set ``worker_processes  auto;``? ``worker_processes  auto;`` detect automatically the number of cpu core and start worker processes as many.