Adds option to retrieve available query stats

Adds a third, optional, parameter 'includeStats'.  When set to true, the search returns an object containing various stats from the query, instead of just the results.
```
index.search( { lastname:smi* }, { start: 0, rows: 3 } , true)
might return:
{
    total:2750,
    maxScore:0.78,
    start:0,
    qTime: 6,  // milliseconds
    docs: [
        { firstname: 'John', lastname: 'Smith' },
        { firstname: 'Sarah', lastname: 'Smitherson' },
        { firstname: 'Bob', lastname: 'Sminerman' }
      ]
}