Made the re/undo code from the branch work in this, this is a manual copy as something went horribly wrong with the repository. Before building I first want to check if everything is there.[skip ci]

GreenshotPlugin/Interfaces/Drawing/IMemento.cs

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+/*
+ * Greenshot - a free and open source screenshot tool
+ * Copyright (C) 2007-2015 Thomas Braun, Jens Klingen, Robin Krom
+ * 
+ * For more information see: http://getgreenshot.org/
+ * The Greenshot project is hosted on Sourceforge: http://sourceforge.net/projects/greenshot/
+ * 
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 1 of the License, or
+ * (at your option) any later version.
+ * 
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ * 
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+using System;
+
+namespace Greenshot.Memento {
+	/// <summary>
+	/// Description of IMemento.
+	/// </summary>
+	public interface IMemento : IDisposable {
+	    /// <summary>
+	    /// Restores target to the state memorized by this memento.
+		/// </summary>
+		/// <returns>
+		/// A memento of the state before restoring
+		/// </returns>
+		IMemento Restore();
+		
+		/// <summary>
+		/// Try to merge the current memento with another, preventing loads of items on the stack
+		/// </summary>
+		/// <param name="other">The memento to try to merge with</param>
+		/// <returns></returns>
+		bool Merge(IMemento other);
+	}
+}