#637 Conversion to use ImageSharp rather than System.Drawing.Common for cross platform compatibility.

Breaking Changes:

* `System.Drawing.Common` is dropped and `SixLabors.ImageSharp` is introduced.
* uses of `NativeImage.CreateFromBitmap(bitmap, options);` is no longer supported, will cause failed builds.

Unexpected Behaviors:

* uses ToDataUrl will always create png data urls, unexpected output may happen for those that manipulate this output expecting a different data url format.

Obsoletions:

* `CreateFromBitmapOptions` & `CreateFromBufferOptions` have been consolidated into `CreateOptions`. Implicit conversions added to ease transition.
* `ToBitmapOptions`, `ToDataUrlOptions`, `ToPngOptions` & `BitmapOptions` have been consolidated into `ImageOptions`. Implicit conversions added to ease transition.

ElectronNET.API/Entities/ToBitmapOptions.cs

@@ -1,13 +1,20 @@
-namespace ElectronNET.API.Entities
+using System;
+
+namespace ElectronNET.API.Entities
 {
     /// <summary>
     /// 
     /// </summary>
+    [Obsolete("Use ImageOptions instead.")]
     public class ToBitmapOptions
     {
         /// <summary>
         /// Gets or sets the scalefactor
         /// </summary>
-        public float ScaleFactor { get; set; } = 1.0f;
+        public float ScaleFactor { get; set; } = NativeImage.DefaultScaleFactor;
+        /// <summary>
+        /// Utility conversion for obsolete class
+        /// </summary>
+        public static implicit operator ImageOptions(ToBitmapOptions o) => new () {ScaleFactor = o.ScaleFactor};
     }
 }