fizzbuzz: *targets* -> *factors*

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
fizzbuzz: Lift out multiple-of?

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>
fizzbuzz: Implement contains-number?

The contains-number? function returns true if x is such a number that n
appears as one of its digits.

The contains-or-is-multiple-of? function combines this and multiple-of?,
returning when either is true.

Signed-off-by: Gergely Nagy <algernon@madhouse-project.org>