Fix relative path issue #293

Added option 'basepath' so that long filenames in the reports can be avoided. For example, by passing '/foo/bar/' as basepath, paths like '/foo/bar/src/index.js' will be transformed into 'src/index.js'.
Ah, nvm.  I see later this was changed to:

```
                if (reporter_options && reporter_options.shortnames){
                    inputFilename = filename.replace(path.dirname(filename),"");
                }
```

And that fixes the problem.  Can there be a npm version update to propagate this change?