updated list-tables to return a lazy sequence of table names.  This
will continue to fetch in the default batch size of 100, but now
returns a lazy sequence, rather than a vector.
Update list-tables function to support > 100 results

The dynamodb client by default only returns 100 results
on a list table request.  To support retrieving more
than 100 results, list-tables has been updated to return
a lazy seq of table names.

- update list-tables to return a lazy seq of table names
  which will continue to page at the default batch size
  of 100
Merge pull request #29 from marcuswr/master

`list-tables` support for > 100 tables (@marcuswr, @paraseba)