Added common interface for distributions

FastRng/Distributions/IDistribution.cs

@@ -0,0 +1,12 @@
+using System.Threading;
+using System.Threading.Tasks;
+
+namespace FastRng.Distributions
+{
+    public interface IDistribution
+    {
+        public IRandom Random { get; set; }
+
+        public Task<double> GetDistributedValue(CancellationToken token);
+    }
+}