Some useful advice, even to someone not writing in Scala, especially sections like published interfaces.

> When defining an interface to a package someone else will use...

> 1. The simplest interface to a package is static method with standard types

> 2. Next, static methods that take/return custom types, presumably with methods

> 3. Next, is needing the user to instantiate some classes

> 4. Lastly, is needing the user to inherit from some classes