Added qseq support

[vgautamm]

Datomis's qseq is primarily useful when you know in advance that you do not need/want a realized collection. i.e. you are only going to make a single pass (or partial pass) over the result data.

Item transformations such as pull are deferred until the seq is consumed. For queries with pull(s), this results in:​

Reduced memory use and the ability to execute larger queries. Lower latency before the first results are returned.

[whilo]

Thanks for opening this issue! Yes we plan to support lazy queries in our redesign of our query engine after our next release (which is pending).