by adding runner plugins for them.
benchmark/lib/benchmark_driver/runner/peak.rb: added peak runner plugin
benchmark/lib/benchmark_driver/runner/size.rb: added size runner plugin
common.mk: allow using them
benchmark/memory_wrapper.rb: deleted in favor of those runner plugins
benchmark/README.md: document them
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@63924 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
