Added various extensions.

Added coding style helpers.
Unit tests.

SystemExtensions.NetStandard/Extensions/BytesExtensions.cs

@@ -0,0 +1,24 @@
+using System.IO;
+
+namespace System.Extensions
+{
+    public static class BytesExtensions
+    {
+        public static byte[] ReadAllBytes(this Stream stream)
+        {
+            if (stream is null) throw new ArgumentNullException(nameof(stream));
+
+            var buffer = new byte[256];
+            using (MemoryStream ms = new MemoryStream())
+            {
+                int read;
+                while ((read = stream.Read(buffer, 0, 256)) > 0)
+                {
+                    ms.Write(buffer, 0, read);
+                }
+
+                return ms.ToArray();
+            }
+        }
+    }
+}