Add differentiable agent based model

See e.g. [StochasticAD.jl](https://github.com/gaurav-arya/StochasticAD.jl), [GradABM](https://github.com/AdityaLab/GradABM), [Blackbirds](https://github.com/arnauqb/blackbirds) (with tutorial [here](https://largeagentcollider.github.io/icaif_tutorial/)), [AgentTorch](https://github.com/AgentTorch/AgentTorch), [DeepABM](https://github.com/mitmedialab/DeepABM-Pandemic)