Improve handling of maximum number of knots
In the spline-based adjustment approach of midas, the maximal allowable number of knots is an important parameter. Up to now, we have tried to set a reasonable upper limit, but any constant leads to occasional problems with badly behaved or special data.
In the future, this parameter should be set in the configuration (cf #7), but for now, let's wire the parameter out and set the default to the highest possible value, i.e. number of data points + 2 * degree of the polynomial.