Add support for postgres instead of mysql. Change sql accourdingly. blob + varbinary -> bytea. No support for UNSIGNED or CREATE INDEX IF NOT EXISTS.

SYN-339: Cancel the notifier timeout when the notifier fires

Handle the fact that events can be persisted out of order, and so to get
the "current max" stream token becomes non trivial - as we need to make
sure that *all* stream tokens less than the current max have also
successfully been persisted.

Improve get event cache

Hotfixes v0.8.1 r3

Don't yield on notifying all listeners

Fix a notifier leak