Include benchmark extension

My JUnit 5 demo contains a benchmark extension that very naively uses System.currentTimeMillis() to report a test’s wall clock time. Use:

@Test
@Benchmark
void benchmarked() throws InterruptedException {
	Thread.sleep(100);
	assertTrue(true);
}

Output:

timestamp = 2018-07-28T09:53:39.128030, Benchmark = Test 'benchmarked()' took 101 ms.
timestamp = 2018-07-28T09:53:39.136931, Benchmark = Test container 'BenchmarkTest' took 152 ms

I think this is worthy for inclusion in JUnit Pioneer. Thoughts?

[fduminy]

Maybe you should use java.time.Clock and its subclasses (I also found one from junit5 : org.junit.platform.console.tasks.IncrementingClock) or Guava’s Stopwatch and Ticker

[nipafx]

To not have this issue open forever, we decided to close it. If other performance-related extensions show up, we can always reopen it.