Draft of iterator and enumerator (CityOfZion/neo-storm#26)

* Draft of iterator and enumerator

* Added iterator API to the syscall mapping

* Added draft of the enumerator.go file

* Added enumerator interop API.

* Updated the changelog

Imported from CityOfZion/neo-storm (156093318b8612e810965bb1ea26e1babfb46cdd).

interop/enumerator/enumerator.go

@@ -0,0 +1,29 @@
+package enumerator
+
+// Package enumerator provides function signatures that can be used inside
+// smart contracts that are written in the neo-storm framework.
+
+// TODO: Check enumerator use cases and add them to the examples folder.
+
+// Enumerator stubs a NEO enumerator type.
+type Enumerator struct{}
+
+// Create creates a new enumerator from the given items.
+func Create(items []interface{}) Enumerator {
+	return Enumerator{}
+}
+
+// Next returns the next item in the iteration.
+func Next(e Enumerator) interface{} {
+	return nil
+}
+
+// Value returns the enumerator value.
+func Value(e Enumerator) interface{} {
+	return nil
+}
+
+// Concat concats the 2 given enumerators.
+func Concat(a, b Enumerator) Enumerator {
+	return Enumerator{}
+}