Output model weighted mrgs

[ceciliaferrando]

Adding a few changes to output AIM model in addition to synthetic data, and support weighted marginals in workload.

run() outputs the AIM model and the synthetic data, with option to specify number of synthetic data samples.

workload comprises (clique, weight) tuples.

compile_workload() accounts for weights in score computation.

In run(), user can provide custom initial_cliques (e.g. marginals containing target) for intelligent initialization. If None, 1-way marginals are used.

Added max_iters argument.

[ryan112358]

Thanks for the PR, looks great!