Convert a string to spinal case.
Spinal case is all-lowercase-words-joined-by-dashes.
spinalCase("This Is Spinal Tap") should return the string this-is-spinal-tap.
spinalCase("thisIsSpinalTap") should return the string this-is-spinal-tap.
spinalCase("The_Andy_Griffith_Show") should return the string the-andy-griffith-show.
spinalCase("Teletubbies say Eh-oh") should return the string teletubbies-say-eh-oh.
spinalCase("AllThe-small Things") should return the string all-the-small-things.