Make /tools/improve script measure speed 5 times and compute an average
Make /tools/improve script measure speed 5 times and compute an average

I measured speed 5 times manually too before introducing the script. It
gives more stable results.

pegjs/pegjs,Mingun/pegjs,GerHobbelt/pegjs,GerHobbelt/pegjs,jlturner/pegjs,pegjs/pegjs,wwall/pegjs-fn,Sciumo/pegjs,Mingun/pegjs,jlturner/pegjs,wwall/pegjs-fn,crguezl/pegjs,mcanthony/pegjs,mcanthony/pegjs,luisvt/pegjs,Sciumo/pegjs,crguezl/pegjs,luisvt/pegjs