When first designing Spina, we made onRender() and onInitialRender()

public methods, when they really should have been protected methods,

discouraging any use outside of subclasses.
This changes them to protected. As this is an interface change, we'll be

making this release 3.0 instead of 2.1. That's a better fit for some of

the other changes introduced in this release anyway. A future change

will formalize the version bump.

Unit tests pass.