RTT percentiles

[giubacc]

Add a section in stats node to add RTT percentiles.
The user should be able to define a time span used to collapse single RTT values into RTT ranges.

Eg:

input:

stats: {
  out: {
    format: {
      rtt_percentile_time_span: 100
    }
  }
}

output:

stats: {
  rtt_percentiles: {
      "45:105" : 10,
      "107:204" : 22,
      "224:310" : 43,
      "516:602" : 86,
      "1450:1549" : 95,
      "1550:1649" : 99,
      "1670" : 100
   }
}