This is mostly a bugfix release, but it gets a minor version bump due to
a single change of behavior: dates and timestamps which mysql may
accept, but are considered invalid (0000-00-00 is a notable example)
previously had inconsistent behavior. Now we convert these to NULL.
- heartbeats have moved into their own table
- more fixes around alibaba rds
- ignore DELETE statements that are output for MEMORY tables upon server
- allow pointing maxwell to a pre-existing database