Add Dice2010 models
Rename base models (mixins)
Remove Dice2007 defaults
Format model names; give population[0] a value
Move population_growth to pandas (endogenous population in 2010)
Update productivity_growth equation
Subclass Dice2007 and 2010
Subclass parameters for 2007 an 2010
Very basic API stub
Merge branch 'api' into develop