Add implementation for WrapMode initializer.

Sources/Core/Model/Enumerations/WrapMode.swift

@@ -38,6 +38,17 @@ public enum WrapMode: GtkWrapMode, RawRepresentable {
     /// Initialize from the GtkWrapMode.
     /// - Parameter rawValue: The GtkWrapMode.
     public init?(rawValue: GtkWrapMode) {
-        nil
+    	switch rawValue {
+    	case GTK_WRAP_NONE: 
+    		self = .none
+    	case GTK_WRAP_CHAR: 
+    		self = .char
+    	case GTK_WRAP_WORD: 
+    		self = .word
+    	case GTK_WRAP_WORD_CHAR: 
+    		self = .wordChar
+    	default: 
+    		return nil
+    	}
     }
 }