[WIP] Implement support for secondary index reads

so basically overall workflow will be, 
1. fetch n rows from index 
2. build main data query (in .then())  
3. For each n rows in index rows array
        1. stream first n+n/4 rows of main data 
        2. compare then with index rows
        3. if matches put them to an array
        4. else stream another row
        5. if no of matched row is equal to req.limit (n)
        6. stop  streaming