(PDB-660) Enable event streaming and provide other streaming cleanups

This provides streaming for the events end-point, thus removing the need for
event-resource-limit setting as well.

Some other cleanups around streaming have been provided also:

* stream-json-results is better documented
* remove-all-environments/remove-environment has been moved into query to
  align with how it is used in src/
* Positioned with-transacted-connection closer to count query and removed it
  from streamed-query-result so that the two db connections were clearly marked
  out in one place (the http code).
* lots of cases of :use converted to :require
* streamed-query-result no longer returns a function, never really needed to.
  The code is somewhat simpler now.
* munge-result-rows for events has now been moved into query so there is only 1
  place where munging is performed. Same for resources.

Signed-off-by: Ken Barber <ken@bob.sh>