VM: Add stackItems; Array, Boolean, Int and ByteArray

pkg/vm/stack/array.go

@@ -0,0 +1,13 @@
+package stack
+
+// Array represents an Array of stackItems on the stack
+type Array struct {
+	*abstractItem
+	val []Item
+}
+
+// Array overrides the default implementation
+// by the abstractItem, returning an Array struct
+func (a *Array) Array() (*Array, error) {
+	return a, nil
+}