Parameterless constructor is added

Author: sakno

src/DotNext.Tests/Buffers/MemoryWriterTests.cs

@@ -146,7 +146,7 @@ public static void ReadWriteUsingArray()
         [Fact]
         public static void StreamInterop()
         {
-            using var writer = new PooledArrayBufferWriter<byte>(ArrayPool<byte>.Shared, 25);
+            using var writer = new PooledArrayBufferWriter<byte>();
             var span = writer.GetSpan(10);
             new byte[]{0, 1, 2, 3, 4, 5, 6, 7, 8, 9}.AsSpan().CopyTo(span);
             writer.Advance(10);

src/DotNext/Buffers/PooledArrayBufferWriter.cs

@@ -40,6 +40,15 @@ public PooledArrayBufferWriter(ArrayPool<T> pool)
             buffer = Array.Empty<T>();
         }
 
+        /// <summary>
+        /// Initializes a new writer with the default initial capacity and <see cref="ArrayPool{T}.Shared"/>
+        /// as the array pooling mechanism.
+        /// </summary>
+        public PooledArrayBufferWriter()
+            : this(ArrayPool<T>.Shared)
+        {
+        }
+
         /// <summary>
         /// Gets the total amount of space within the underlying memory.
         /// </summary>