Expand data to include longer durations

[kevinykuo]

SOA2015 actually uses duration (in the form (Duration - 9)^(-n) for n = 1, 2, 3) as a predictor and claims that

This model also extends beyond the initial shock lapse all the way to duration 19

The dataset they provided doesn't really support this, as

> table(insurance::lapse_study$duration)

    10     11     12    13+    6-9 
 59730  29659  19233  35069 201936 

we'll do our best here and take 10, 11, and 12, and convert those to numeric