Multi-field cursor support

[darh]

Very nice work! I'm regretting not finding you guys 2y ago and and ended up doing something half-way on my own (. I would very like to get rid of that and migrate away from home-brew db-handling code for our product (https://github.com/cortezaproject/corteza-server/) and achieve better multi-db support.

From what I see after doing some research and experimenting there is one thing that prevents me: multi-field cursor support. We've invested quite some time to implement it on our end and I'm positive we can port it to upper/db if there is interest?

Or.. if someone else has already done it... even better.