Add benchmarks that show transpilation + minification times

What people actually care about w.r.t. build times is usually the end-to-end time. Talking with @skevy, we were saying a typical production build pipeline will transpile and minify, which previously entailed running Babel (ex: with es2015 preset) and then Uglify. But now a pipeline could run just Babel (ex: with es2015 + babili).

The perf benchmarks currently make Uglify look way better than Babili to people who prefer 1.5-2x faster build times for roughly the same end result, but if the actual end-to-end build times that comprise transpilation and minification are faster, that'd change a lot of minds.