new proposed 'capitalize' implementation

This would capitalize the first character and downcase the rest.
for example, "wHoAaA!" -> "Whoaaa!"

Maybe capitalize should take an optional second argument wrt this behavior?

eg:
`Humanize.capitalize("wHoAaA") // "WHoAaA"`
but
`Humanize.capitalize("wHoAaA", true) // "Whoaaa"`