Use a more idiomatic trait-based implementation of serialization for treemaps

[Dr-Emann]

See #108

Makes the changes from #106 for treemap.

This also adds some more doc comments to serialization types/functions, and does some misc clippy fixes for treemap functions.

[saulius]

This is great, @Dr-Emann. Looks like this was the last piece for 1.0 right?