benchmark_driver/runner: add runners for metrics

supported by legacy benchmark/driver.rb.

benchmark/README.md: document them

common.mk: update benchmark_driver to correct 0.0 output and to fix
spacing format of `-o simple` and `-o markdown`.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63933 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

benchmark/lib/benchmark_driver/runner/cutime.rb

@@ -0,0 +1,22 @@
+require 'benchmark_driver/runner/total'
+
+class BenchmarkDriver::Runner::Cutime < BenchmarkDriver::Runner::Total
+  METRIC = BenchmarkDriver::Metric.new(name: 'cutime', unit: 's', larger_better: false)
+
+  # JobParser returns this, `BenchmarkDriver::Runner.runner_for` searches "*::Job"
+  Job = Class.new(BenchmarkDriver::DefaultJob)
+  # Dynamically fetched and used by `BenchmarkDriver::JobParser.parse`
+  JobParser = BenchmarkDriver::DefaultJobParser.for(klass: Job, metrics: [METRIC])
+
+  private
+
+  # Overriding BenchmarkDriver::Runner::Total#metric
+  def metric
+    METRIC
+  end
+
+  # Overriding BenchmarkDriver::Runner::Total#target
+  def target
+    :cutime
+  end
+end