Producing better benchmark time information

[purbon]

We're actually using Benchmark.realtime in order to get time information for each run, this might be misleading in case of a competition for cpu cycles.

Will be interesting to use the cpu cycle as time, we can get more information by:

• Using a system call like _times_.
• Or using _getrusage_.

We should investigate the better usage of this under with jruby and/or MRI.

[jordansissel]

Before I removed the code, Stud used to have a benchmark feature that invoked getrusage -

• FFI implementation: https://github.com/jordansissel/ruby-stud/blob/f93006cffb15e317f6bbb763879b4e9df0fd5e35/lib/stud/benchmark/rusage.rb
• Usage: https://github.com/jordansissel/ruby-stud/blob/f93006cffb15e317f6bbb763879b4e9df0fd5e35/lib/stud/benchmark.rb#L29-L44

[purbon]

@jordansissel nice, very interesting.