Include the benchmarking code itself in the Suite (for display)

It might be very nice to include the actual benchmarking code that benchee was run with in the suite itself so it can be displayed by formatters (for instance in the html formatter) for an easy reference as to what the benchmark actually looked like.

I'm not sure how easy it is though... is there some magic variable like "actual top level file that is executing" ;P I guess we can try and grab it from the command being run but that might also be error prone and should definitely have a fail safe.

Start by tracing how the benchmark suite is built and how formatters, especially the HTML formatter, consume it. Investigate whether the command or executing file can provide the benchmarking source, including a safe fallback; done means the source is available in the suite and can be displayed by formatters.

Written by the indexing model from the issue text.