Added support to report inner errors

This PR adds support to report inner errors.

Nevertheless, I'm also thinking that the extract error message function should be a fallback to an optionally user defined function when configuring the plug-in.

Basically it would be used:
```javascript
function customErrorMessageExtractor(error, defaultMessageExtractor){
  if (canExtractError(error)) { /* do so and return */ }
  return defaultMessageExtractor(error);
}
```

And also if no custom extractor is defined the default one would be used.

Thoughts?