Rayon **find_map_any()** demonstration program

This small program shows how effective and simple Rust's *Rayon* crate **find_map_any()** can
be used to utilize all CPU cores. 

P.S.: The `factorize_iterative()` function of mine was an experiment to try out *find_map_any()*
with something not immediately trivial, but is of course not meant for production use.  Better and 
faster algorithms exist, also in crates.io.