Tests with empty geometries

[kylebarron]

The format specifies that empty geometries (which are not the same as missing!) have an empty inner array.

We need to make sure that this works with the layout I have, and we should also make sure that is_empty is accurate for this!

Also an empty point is defined with NaN values, so we should validate that (and write a custom PartialEq probably)

[kylebarron]

An empty point has two values NaN, NaN from #81