Made the Win10 share work, at least somewhat.

GreenshotWin10Plugin/MemoryRandomAccessStream.cs

@@ -0,0 +1,69 @@
+using System.IO;
+using Windows.Storage.Streams;
+
+namespace GreenshotWin10Plugin
+{
+	public sealed class MemoryRandomAccessStream : MemoryStream, IRandomAccessStream
+	{
+		public MemoryRandomAccessStream()
+		{
+		}
+
+		public MemoryRandomAccessStream(byte[] bytes)
+		{
+			Write(bytes, 0, bytes.Length);
+		}
+
+		public IInputStream GetInputStreamAt(ulong position)
+		{
+			Seek((long)position, SeekOrigin.Begin);
+
+			return this.AsInputStream();
+		}
+
+		public IOutputStream GetOutputStreamAt(ulong position)
+		{
+			Seek((long)position, SeekOrigin.Begin);
+
+			return this.AsOutputStream();
+		}
+
+		ulong IRandomAccessStream.Position => (ulong)Position;
+
+		public ulong Size
+		{
+			get { return (ulong)Length; }
+			set { SetLength((long)value); }
+		}
+
+		public IRandomAccessStream CloneStream()
+		{
+			var cloned = new MemoryRandomAccessStream();
+			CopyTo(cloned);
+			return cloned;
+		}
+
+		public void Seek(ulong position)
+		{
+			Seek((long)position, SeekOrigin.Begin);
+		}
+
+		public Windows.Foundation.IAsyncOperationWithProgress<IBuffer, uint> ReadAsync(IBuffer buffer, uint count, InputStreamOptions options)
+		{
+			var inputStream = GetInputStreamAt(0);
+			return inputStream.ReadAsync(buffer, count, options);
+		}
+
+		Windows.Foundation.IAsyncOperation<bool> IOutputStream.FlushAsync()
+		{
+			var outputStream = GetOutputStreamAt(0);
+			return outputStream.FlushAsync();
+		}
+
+		public Windows.Foundation.IAsyncOperationWithProgress<uint, uint> WriteAsync(IBuffer buffer)
+		{
+			var outputStream = GetOutputStreamAt(0);
+			return outputStream.WriteAsync(buffer);
+		}
+	}
+}