Be less precise about timings

[mitar]

Currently durations are rendered as:

strconv.FormatFloat(float64(m.Duration)/float64(time.Millisecond), 'f', -1, 64)

I think this is over precise: all digits beyond millisecond? That could even be a security issue as somebody could do timing attacks determining how long some operation is taking (e.g., password checking). I think there is really no point in sending more than 1 extra digit after milliseconds. I mean, how precise those measurements are anyway, no? They are not an average of multiple measurements.

So I suggest:

strconv.FormatFloat(float64(m.Duration)/float64(time.Millisecond), 'f', 1, 64)

I could be convinced to increase 1, but not to have it unbounded.

[mitar]

I made #25.