Support JSON formatted server statistics: op=stats&options=json

Hockeypuck's status page contains most of the info needed for SKS statistics aggregators, but the HTML is different. It would be better to provide this data in JSON format.

{
  "hostname" : "",
  "server_contact" : "",
  "recon_port" : "",
  "numkeys" : "",
  "software" : "",
  "version" : "",
  "peers" : [ "", "", "" # repeats for each peer hostname
  ]
#For completeness, we could add (allow for):
  "mailsync_peers" : [ "", "", "" # repeats for each peer email address
  ],
   "stats_by_day" : [
    {
          "time" : "",
          "new_keys: : "",
          "updated_keys": ""
        } # Object repeats for each row of table
  ],
  "stats_by_hour" : [
    {
          "time" : "",
          "new_keys: : "",
          "updated_keys": ""
        } # Object repeats for each row of table
   ]
}

nodename, http_port and debug_level should also be provided to support https://github.com/syscomet/sks_spider.

This will be returned when options=json is specified in the request.