Copy should work as a function

If copy is a function bound to the view, then it needs to be called with
a single object that will be destructed, otherwise the params will
remain undefined.

src/dragula-and-drop.js

@@ -43,7 +43,8 @@ export class DragulaAndDrop {
       isContainer: this._isContainer.bind(this),
       moves: this._moves.bind(this),
       accepts: this._accepts.bind(this),
-      invalid: this._invalid.bind(this)
+      invalid: this._invalid.bind(this),
+      copy: this._copy.bind(this)
     };
 
     this.options = Object.assign(aureliaOptions, boundOptions);
@@ -132,10 +133,19 @@ export class DragulaAndDrop {
     }
   }
 
+  _copy(item, container) {
+    if (typeof this.copy === 'function') {
+      return this.copy({ item, container });
+    }
+    if (typeof this.globalOptions.copy === 'function') {
+      return this.globalOptions.copy({ item, container })
+    }
+    return this._convertToBooleanIfRequired(this._getOption('copy'))
+  }
+
   _setupOptions() {
     let result = {
       containers: this._getOption('containers'),
-      copy: this._convertToBooleanIfRequired(this._getOption('copy')),
       copySortSource: this._convertToBooleanIfRequired(this._getOption('copySortSource')),
       revertOnSpill: this._convertToBooleanIfRequired(this._getOption('revertOnSpill')),
       removeOnSpill: this._convertToBooleanIfRequired(this._getOption('removeOnSpill')),