Benchmark against other engines

[cpq]

[mkmik]

Basic framework added in #376. TODO:

• [ ] write some meaningful benchmarks
• [ ] write some C<->js benchmarks
• [x] execute the benchmark container on our dev machine
• [ ] Add docs/benchmark.adoc with a short description of measuring method and results

[mkmik]

Current benchmark results available at http://dev.cesanta.com:5672/

[cpq]

Added action item to document benchmark method. We also need to show benchmark result in our documentation - either by embedding graphs there, or by referencing an external page with the results.