Fixed several issues and improved it again

Couple of things:

1. not sure if you saw it, but on a scanDynamoDBWithUnion(query) method was calling the old method upon fetching next set of items, fixed

2. headers were written to a file twice , added a fix that would write only once

3. with this code, you can add Limit back but it will fail on describe , fixed :)

Please pull.

thanks
Merge pull request #1 from jeveloper/patch-2

Fixed several issues and improved it again