Often in program logic, multiple different steps need to be taken that
are independent of each other, but their total result is needed before
the next step can be taken.  In synchronous code, the usual approach is
to perform them sequentially.

An asynchronous or event-based program could do this, but if each step
involves some I/O idle time, better overall performance can often be
gained by running the steps in parallel.  Async::MergePoint object can
then be used to wait for all of the steps to complete, before passing
the combined result of each step on to the next stage.

This module was originally part of the IO::Async distribution, but was
removed under the inspiration of Pedro Melo's Async::Hooks distribution,
because it does not itself contain anything I/O-specific.