Added posibility to override the test-name of a problem so you can implement different alternatives:
  euler(problem1, Some("Problem 1 Alternative 1")) { ... }
  euler(problem1, Some("Problem 1 Alternative 2")) { ... }
Added posibility to override the test-name of a problem so you can implement different alternatives:
  euler(problem1) { ... }
  euler(problem1, Some("better performance alternative")) { ... }
using default String "" instead of None
(less code on usage site)