Allow clauses to be specified for each record in insert-batch

The old syntax is still supported.
An additional clause (e.g. where or using) can be specified
individually for each record.  That record should be wrapped
in a vector (any seq really).  Records without additional
clauses are stilled supported and don't need to be wrapped.
Merge pull request #18 from samn/insert-batch-clauses

Allow clauses to be specified for each record in insert-batch