Custom sinks

It is nice to put the results from benchmark runs in version control so that perf can be tracked over time.
Currently I hack it like this:

``` c#
using System.Collections.Generic;
using System.IO;
using BenchmarkDotNet.Reports;
using BenchmarkDotNet.Running;

public class Program
{
private static readonly string DesinationDirectory = System.IO.Path.Combine(new DirectoryInfo(Directory.GetCurrentDirectory()).Parent.Parent.FullName, "Results");

public static void Main()
{
foreach (var summary in RunAll())
{
CopyResult(summary.Title);
}
}

private static IEnumerable RunAll()
{
ClearAllResults();
var switcher = new BenchmarkSwitcher(typeof(Program).Assembly);
var summaries = switcher.Run(new[] { "*" });
return summaries;
}

private static IEnumerable RunSingle()
{
var summaries = new[] { BenchmarkRunner.Run() };
return summaries;
}

private static void CopyResult(string name)
{
#if DEBUG
#else
var sourceFileName = System.IO.Path.Combine(Directory.GetCurrentDirectory(), "BenchmarkDotNet.Artifacts", "results", name + "-report-github.md");
System.IO.Directory.CreateDirectory(DesinationDirectory);
var destinationFileName = System.IO.Path.Combine(DesinationDirectory, name + ".md");
File.Copy(sourceFileName, destinationFileName, true);
#endif
}

private static void ClearAllResults()
{
if (Directory.Exists(DesinationDirectory))
{
foreach (var resultFile in Directory.EnumerateFiles(DesinationDirectory, "*.md"))
{
File.Delete(resultFile);
}
}
}
}
```