Add cScore and cScore1 metrics.

Also tweak consistencyStat and consistencyStat2 to use numpy (and share code with each other and cScore), and clean up some other functions a bit.

From descriptions in FAQ:

The <b>cScore</b> metric is a way of combining amount of sleep with consistency: it's the product of avg and consistent. Another way to look at this is that it's an average of your sleep weighted by time of day, where the weight associated with a time corresponds to the probability that you were asleep at that time on a random day.

The <b>cScore1</b> metric is another way of combining sleep with consistency. This is the average of your sleep only counting when you were asleep at the same time of day twice in a row, or equivalently, how much your sleep times overlap from each day to the next. So named because it's a variant on cScore where the weight only depends on the times you were asleep on the previous day, rather than your distribution of sleep over all days.