The switching station and supply converter only semantically connect to
cables in particular directions. Make them visually connect only in
the matching directions. This is done by special-casing in the cable
update logic. If more irregular items arise in the future, or the
existing items start to need facedir logic, this should be generalised
into something like the connect_sides system for pneumatic tubes.
Expand list of sections yet to be written. Arrange sections both written
and unwritten into a two-level structure, with a bit of consequential
reordering.
Added sections on the technic-specific kinds of item processing, and on
generic metal mechanics, and the specific trickery around iron (merging
in notes_on_iron).
Vanessa finds "altitude" to carry too much of an aviation connotation.
Zefram finds "elevation" to carry insufficient connotation of being
relative to sea level, so also adds a clarifying note. Beware of changing
this terminology without negotiation, as it aroused surprisingly strong
opinions.
