Change growth rate from 1.5x to 2x; #1100

2x is easier to compute in your head than 1.5x, is nice and geeky, and
gets you to a reasonable salary (~$1,000/wk) within a more reasonable
time (10 weeks ~= 2.5 months vs. 17 weeks ~= 4+ weeks), while still
giving 6 weeks or so of relatively low numbers to build trust.
Bump version to 9.3.31
Bump version to 9.3.31-dev