Add a method to allow ADCIRC to drive the NN model

We need add a `coupler_run_adcirc_driving_nn()` method to the `AdcircNN` class to allow ADCIRC to drive the neural network. This is needed to enable one-way `Adn` and `AdndA` coupling. Likewise, `nn_init_bc*` and `nn_set_bc_*` functions must be also be added for the same. I am addressing these in PR #5.