* Refactor get_next_coords().
- I don't see too much point to it. It is working as it is, and it's
only one function that doesn't affect the rest of the code.
* Create a base class for classes with 'subs' functionality - like
get_nth_sub, add_sub, num_subs, etc. Both ..::Node and ..::Item share it.
- They have slightly different semantics, and besides - it's not
too much duplicate code. It would be more trouble than it's worth.
* Future direction: generate the tree once and then be able to render
it for different path_info()/current_host() configurations. (and the
generated tree re-used by all other members).
- the problem is that the expand() operations and the expanded()
flag depends on this combination. Thus, the generated tree is
different for any path_info()/current_host().