- Add zoom feature (view point distinct from root).
- Add receptacles (leaves with NULL client pointer).
- Handle window size constraints specified by size hints.
- Add support for showing/hiding nodes.
- Implement all the MUSTs in the EWMH specification.
- Set more attributes in `make_client` (instead of doing it in `apply_rules`) and don't pass `XCB_NONE` as argument.
- Use BSD `sys/{queue/tree}.h` for {list,tree} structures?
- Handle malloc failure everywhere.
