This commit changes "deno bench" subcommand, by updating
the "Deno.bench" API as follows:
- remove "Deno.BenchDefinition.n"
- remove "Deno.BenchDefintion.warmup"
- add "Deno.BenchDefinition.group"
- add "Deno.BenchDefintion.baseline"
This is done because bench cases are no longer run fixed amount
of iterations, but instead they are run until there is difference between
subsequent runs that is statistically insiginificant.
Additionally, console reporter was rewritten completely, to looks
similar to "hyperfine" reporter.
