Ignore the compilation output directory.
Hello, trait!

My first ever Scala trait!
Add a Philosophical Frog.

Mixing in just one trait feels a little bit like extending a superclass.
Mix in Philosophical when Frog alredy extends Animal.

Here, the syntax differs from just extending a trait with no
superclass, and looks different than anything previous.
Mix multiple traits in to Frog.
Override methods inherited from traits.