Option to fetch only checkins more recent than the current max checkin

[dogsheep]

Option to fetch only checkins more recent than the current max checkin

[simonw]

Also needed: an option for "fetch all checkins created within the last X days".

This should help provide support for that Swarm feature where you can retroactively checkin to places in the past.

[simonw]

https://developer.foursquare.com/docs/api/users/checkins documents afterTimestamp:

Retrieve the first results to follow these seconds since epoch. This should be useful for paging forward in time, or when polling for changes. To avoid missing results when polling, we recommend subtracting several seconds from the last poll time and then de-duplicating.

[simonw]

I'm going to go with --since=1d/2w/3h for this.

[simonw]

Documented here: https://github.com/dogsheep/swarm-to-sqlite/blob/0.2/README.md#usage