Add YGLayoutGetMargin

Summary:
Fix #326. I'll open another PR once this one gets accepted to add support for `YGLayoutGetBorder` 👌
Closes https://github.com/facebook/yoga/pull/335

Reviewed By: gkassabli

Differential Revision: D4409399

Pulled By: emilsjolander

fbshipit-source-id: 8153f6701cab60b55a485f6d2e0b9f7767481090

csharp/Facebook.Yoga/YogaNode.Spacing.cs

@@ -452,6 +452,54 @@ namespace Facebook.Yoga
             }
         }
 
+        public float LayoutMarginLeft
+        {
+            get
+            {
+                return Native.YGNodeLayoutGetMargin(_ygNode, YogaEdge.Left);
+            }
+        }
+
+        public float LayoutMarginTop
+        {
+            get
+            {
+                return Native.YGNodeLayoutGetMargin(_ygNode, YogaEdge.Top);
+            }
+        }
+
+        public float LayoutMarginRight
+        {
+            get
+            {
+                return Native.YGNodeLayoutGetMargin(_ygNode, YogaEdge.Right);
+            }
+        }
+
+        public float LayoutMarginBottom
+        {
+            get
+            {
+                return Native.YGNodeLayoutGetMargin(_ygNode, YogaEdge.Bottom);
+            }
+        }
+
+        public float LayoutMarginStart
+        {
+            get
+            {
+                return Native.YGNodeLayoutGetMargin(_ygNode, YogaEdge.Start);
+            }
+        }
+
+        public float LayoutMarginEnd
+        {
+            get
+            {
+                return Native.YGNodeLayoutGetMargin(_ygNode, YogaEdge.End);
+            }
+        }
+
         public float LayoutPaddingLeft
         {
             get