GUE: The Beginning

Turned out that we got all the hard work done: crafting.cpp is robust and handles liquid components no problem.  Just never tried the handoff from construction.cpp before.

Can take it all the way to z-10 now.  Yeah, they're not the same as z+, but it's a start.

And if you get tired of being underground, you can dig back up now.  Same caveat applies: no stairways on the same z-level within about 5 tiles of each other, unless you put them together to make a wider stairway for appearances' sake.

Wouldn't have happened without Kevin's help on the previous stairway project, either.  Continued thanks, man.