* Updates bootstrapper algorithm:
* Change from least-squares solution to find a solution that is closest to a target curve, rather than zero.
Each point on the target curve is derived as the price of the smallest contract that each period is within.
* Zero price is used as piecewise flat price for curve points in gaps. This fixes a bug, where the last price not in a gap is filled in.
* Both bootstrapper and spline return records.
* Spline returns type includes solved parameters.
* Tension parameter added as input to spline, although doesn't work that well.