Nimterop should have a stub option for specified identifiers
Often, nimterop misses some types and compilation fails. The easiest way is to stub those types as:

```
type
  name = object
```

This works fine if the user doesn't intend using those types and simply wants to unblock wrapping. Need to have a way to stub this out via cimport as well as toast.

If it is possible to automatically detect and stub out, will be even cooler. Might work with #160.