Improve appearance of validation output

[YegorStepanov]

Before #2148, like v0.13.2:

Master:

PR:

no validation errors:

Master:

PR:

[YegorStepanov]

What is the purpose of the double slash? Are they meant to show a newline in the console?
For example:

[AndreyAkinshin]

We use double slashes to distinguish user messages from the payload (the results of the measurements).
@adamsitnik can we avoid using slashes with the help of our new Pipe approach?

[YegorStepanov]

can we avoid using slashes with the help of our new #2092?

Yes, if we remove the first line or pass the NullLogger to the broker, the measurements and input from generated project will not be printed.

BenchmarkDotNet/src/BenchmarkDotNet/Loggers/Broker.cs

Lines 45 to 51 in 3906381

	// TODO: implement Silent mode here
	logger.WriteLine(LogKind.Default, line);
	if (!line.StartsWith("//"))
	{
	Results.Add(line);
	}

But how can we distinguish user input from measurements (it requires to implement silent mode)?

[Benchmark]
// I haven't tried this, but it looks like we can break the engine.
public void M() => Console.WriteLine("OverheadJitting  100500: 99 op, 24 h, 0 us/op ");

Because it's just parsing the input:

BenchmarkDotNet/src/BenchmarkDotNet/Reports/Measurement.cs

Lines 105 to 124 in 32bb2de

	/// <summary>
	/// Parses the benchmark statistics from the plain text line.
	///
	/// E.g. given the input <paramref name="line"/>:
	///
	/// WorkloadTarget 1: 10 op, 1005842518 ns
	///
	/// Will extract the number of <see cref="Operations"/> performed and the
	/// total number of <see cref="Nanoseconds"/> it took to perform them.
	/// </summary>
	/// <param name="line">The line to parse.</param>
	/// <param name="processIndex">Process launch index, indexed from one.</param>
	/// <returns>An instance of <see cref="Measurement"/> if parsed successfully. <c>Null</c> in case of any trouble.</returns>
	// ReSharper disable once UnusedParameter.Global
	public static Measurement Parse(string line, int processIndex)
	{
	if (string.IsNullOrWhiteSpace(line) || line.StartsWith(GcStats.ResultsLinePrefix))
	return Error();
	try