Move method into Rust's Euler library.
Move method into C++'s Euler library.
Move method into Clojure's Euler library.
Move method into Go's Euler library.
Move method into Haskell's Euler library.
Move method into Java's Euler library.
Move method into PHP's Euler library.
Move method into Python's Euler library.
Move method into Ruby's Euler library.
Solve problem 15 using PHP/Python/Ruby/Rust.