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
> Do you also gave a suggestion here?

My suggestion, for now, is to use max threads to get the number of hardware threads available for use. If I remember correctly, nginx docs recommend running with `workers = max_threads * 2`, but I'm not enough of an nginx guy to say if that's the best value here.