Recursive struct mapping not supported

Structs that directly or indirectly define themself in the field tree generate a stack overflow in the parsing routine.

```go
type A struct {
  BTest B
}

type B struct {
  ATest A
}
```

The parser should keep track of already visited types in the depth traversal and quit when encountering a loop

A -> B -> A |

This should be part of the Inspect Context