Empty examples on schema reference page / redundant examples

[duncandewhurst]

For example, only the first Classification example renders and only the first six Period examples render.

Relatedly, I'm not sure it's helpful to have, for example, 16 examples of the Period object. We can perhaps modify the pre-commit script to only add up to three examples, but I need to check whether that would result in any useful examples being cut.

[duncandewhurst]

In the interests of getting 0.9.4 out and since the examples are non-normative, I've moved this to the iterative improvements milestone.