extend all pool interfaces to have common constructor

[brandondube]

In some applications, there is read-only global state that needs to be distributed among workers. This can be implemented via multiprocessing.Pool's initializer and initargs options. The nonuniformity of the pool interfaces means that this workflow is not possible on an MPI pool. I think MPI broadcast allows this functionality to be built into this package. Would this addition be possible?

[adrn]

That would be nice to have! Do you want to try implementing? It may take me some time to get to this.