Removed show_console call that was accidentally left in.

Probably added for debugging, it doesn't belong in the tree.  This
fixes #11.
Added support for selecting a # of items in yn_function.  This fixes #1.

There's two principle parts to this change.  First off, I added a new
custom selection mode for menus called PICK_ANY_ONE.  In this mode, you
can select one type of item, and count it up if you want, but you can't
select multiple items.  So it's a kinda of limited PICK_ANY.

I then altered nds_yn_function so that, if the character list passed in
is NULL or contains a '#', then we use PICK_ANY_ONE as the menu mode,
and after an item is selected, we form a string containing the count and
the inventory letter concatenated together.  Finally, we return the
first character of that buffer, and shove the rest into the
newly-refactored input buffer.
Stop map artifacts when changing levels.
Fixed nds_init_map to use nds_clear_map, instead of duplicating that
logic in two places.
Add DEBUG_PRINT macro.

This replaces direct calls to iprintf all over the place.  Just a little
tidying up.