Update CHANGELOG and README

Update the CHANGELOG and README to reflect the new reality that tests
will only pass against Redis 2.8.4. Also record other recent changes.

Change-Id: I52f1a3b7bdf18e5c592bba403d6d634c90b83fef
Reviewed-on: https://gerrit.causes.com/33201
Reviewed-by: Shane da Silva <shane@causes.com>
Tested-by: Shane da Silva <shane@causes.com>