- Makes `tree_next` not recursive.
- Adds `focus next|prev [sibling]` command. See (1.) and (2.) in
https://github.com/i3/i3/issues/2587#issuecomment-378505551 (Issue also
requests move command, not implemented here).
- Directional focus command now supports command criteria.
Wrapping is not implemented inside a floating container. This was also
true before the refactor so I am not changing it here.
Orestis Floros