One rectangle's worth of data: a name and a size, with children inside it. A leaf's size is set
by the caller; a parent's is the sum of its children's, filled in by recompute_if_dirty.
The user_data_ fields are free for the program.
Fields
- name: string
- size: float64
- parent: *Treemap_Node
- children: [..] *Treemap_Node
- user_data_pointer: *void
- user_data_s64: s64
- user_data_float64: float64
- locator: Bucket_Locator