Decode: convert table key to correct type (#741)

Fixes #740.

unmarshaler.go

@@ -412,9 +412,10 @@ func (d *decoder) handleKeyPart(key ast.Iterator, v reflect.Value, nextFn handle
 		elem = v.Elem()
 		return d.handleKeyPart(key, elem, nextFn, makeFn)
 	case reflect.Map:
+		vt := v.Type()
 
-		// Create the key for the map element. For now assume it's a string.
-		mk := reflect.ValueOf(string(key.Node().Data))
+		// Create the key for the map element. Convert to key type.
+		mk := reflect.ValueOf(string(key.Node().Data)).Convert(vt.Key())
 
 		// If the map does not exist, create it.
 		if v.IsNil() {
@@ -431,7 +432,6 @@ func (d *decoder) handleKeyPart(key ast.Iterator, v reflect.Value, nextFn handle
 			// map[string]interface{} or a []interface{} depending on whether
 			// this is the last part of the array table key.
 
-			vt := v.Type()
 			t := vt.Elem()
 			if t.Kind() == reflect.Interface {
 				mv = makeFn()