Add progress reporting to `get_records()`

[PietrH]

get_records() takes a while to run, this is because it currently does two requests including a big one to actually fetch all the records in one go. With filtering #16 we'll need another request.

• We could add a verbose = TRUE argument to keep the user up to date on what the function is doing
• Ideally we'd want some sort of progress bar on the slowest request, I expect this request will get a lot slower/bigger next year. And it's 10MB already.

[PietrH]

I'm filing this for now, this is a nice to have beyond v0.1