Fix bug when growth is estimated externally with par names.

Names from outside estimation routine were not matching. Also the values
were not being passed as numeric. Both bugs are fixed with this commit.
Create bad code in growth_estimation.R but it works.

It was not working with data_ being passed as an argument.
Changed the routine to bad code!!! where the function is inside another
and it looks to the environment to get the data and a3.
This is bad but it works. Need help fixing it to be CRAN appropriate.