Asynchronous programming can be benefitial for performance, however
not all functions are written for nonblocking interaction and
external processes almost never are.

By forking the blocking call into a new process, the main thread may
continue to run non-blocking, while the blocking call evaluates.
Mojo::IOLoop::ForkCall manages the forking and will emit an
event (or execute a callback) when the forked process completes.
Return values are serialized and sent from the child to the parent
via an appropriate pipe for your platform.

Deprecated! Use Mojo::IOLoop::Subprocess instead.