Save confidence intervals as a dictionary

[pberkes]

Fix #136
Fix #142

Confidence intervals are not saved as

>>> result.confidence_intervals['threshold'] 
{
 '0.95' : [0.0041551724137931035, 0.005110079575596817],
 '0.9' : [0.004218832891246685, 0.005110079575596817],
 '0.68' : [0.004346153846153846, 0.004982758620689655]
}

I propose to use '0.95' instead of '95%', because in my experience the latter would mean that we'll be writing forever code that converts '95%' into 0.95 and viceversa

[guillermoaguilar]

This all look good to me.