Enh: option to limit stats.lua output by message count

[sebbASF]

The stats.lua API is not really suited to mobile devices which may have limited data allowances (or limited memory). A mobile user is not likely to want to scroll through a month's worth of data. It's more likely that they will want to review the most recent messages in a few mailing lists.

Whilst the results can be limited by start and end date, even a single day can hold too many messages.

It would be useful to be able to limit the response by size, so the user could request the first N messages going backards from a specific start time (default now ).