Create a method named
max should accept an array of objects that implement
OurComparable and return the maximum.
Require that the array be non-empty.
As a reminder,
compareTo returns a negative integer, zero, or a positive integer as this object is less than,
equal to, or greater than the passed object.
Kotlin also allows you to use comparison operators directly with classes that implement
OurComparable works exactly the same as the official
Comparable interface, except it is slightly simplified
and does not accept a type parameter.