http://danielwestheide.com/scala/neophytes.html
http://danielwestheide.com/blog/2013/02/06/the-neophytes-guide-to-scala-part-12-type-classes.html
http://blog.jaceklaskowski.pl/2015/05/15/ad-hoc-polymorphism-in-scala-with-type-classes.html
http://www.casualmiracles.com/2012/05/03/a-small-example-of-the-typeclass-pattern-in-scala/