Switch From Lazy Vals To null init Pattern

[isomarcte]

Avoid possible Scala 2 synchronization bugs by using the null init pattern instead oflazy vals.

Context: #19 (comment)

[isomarcte]

As noted on #45, when prototyping this we should ensure we are creating the backing vals as private[this] to avoid extra method wrappers generated by the Scala compiler.

[armanbilge]

Ah, I completely forgot we had discussed this before, sorry!

Avoid possible Scala 2 synchronization bugs

Just to clarify: I was more concerned about the performance cost of synchronization, rather than bugs.