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
Ping @msmith-techempower  - what value do you pass for `--max-threads` when doing the benchmarks on the production hardware? The number of cores?