robjhyndman/demography ? reverse-engineered prompt

Build me an R package called demography that helps with common demographic analysis tasks.

I want it to calculate life tables, fit Lee Carter style mortality models, do functional data analysis for mortality, fertility, and net migration, and support stochastic population forecasting. It should feel like a real CRAN ready package, with clean function names, help pages, and examples that show how to use each main feature on simple data.

Please include a basic README, package metadata, and enough internal code structure that the main workflows are easy to follow and extend. If you need to check current R package conventions or best practices, look them up online first. Make sure the package is usable from a fresh install and that the main functions return sensible, well documented results.