[Issue 252] Add type cast for default enum values in C#

When creating a “CreateXxx(...)” method for a “simple table” type,
enum-type fields with a non-zero default must have an explicit
cast for the respective argument default value, because in C#,
there is an implicit cast from int to an enum only for 0.

Also, added an example of such type into the example monster_test
type, so that we test this feature.

tests/MyGame/Example/Any.go

@@ -5,4 +5,5 @@ package Example
 const (
 	AnyNONE = 0
 	AnyMonster = 1
+	AnyTestSimpleTableWithEnum = 2
 )