1. calculate age in days, weeks, and months
2. calculate body mass index for metric and english unities
3. calculate z-score for a given measurement and box-cox parameters (l,
m, s)
4. calculate centile score for a given measurement and box-cox
parameters
Initial implementation to fetch growth indicators from WHO.
For now, the system merges the measurements for each gender and age
group in a single `csv` file.
The final solution should do this, saving a `dets` file.
