Include more info in the meta/stats endpoint.

The meta/stats endpoint returns aggregated downloads
count for the last day, week and month.
It also includes both the stats for the specific
entity revisions and the stats for all revisions of the
requested entity.
The names here are quite long. How about saving some bandwidth by encapsulating the results into a struct?
Even with the backward-compatibility field, it still saves 170 bytes per result, and the correspondence between the two sets of results is more obvious too.

	type StatsResponse struct {
		ArchiveDownloadCount int64 // superceded by ArchiveDownload but maintained for backward compatibility.
		ArchiveDownload StatsCount
		ArchiveDownloadAllRevisions StatsCount
	}
	
	type StatsCount struct {
		Total int64                // Total count over all time.
		Day int64                 // Count over the last day.
		Week int64              // Count over the last week.
		Month int64             // Count over the last month.
	}