Make -r argument more useful.

[eedrummer]

Requested Feature

Synthea currently allows users to specify a reference time, using the -r argument. This argument currently takes a date in YYYYMMDD format. If this argument is being used to reproduce a previous run, it isn't particularly helpful unless that run also used a reference time.

If a user created a "plain" Synthea without specifying a reference date, there is no way to replicate it since Synthea's internal representation of the date is a full time stamp, and not just a date.

It would be nice to change this argument or add another argument that would allow users to pass in a long in the same way it is used in Synthea.

[jawalonoski]

Alternatively, we could make the default reference date not a full time stamp, and round to the day.