src/cavern.h,src/img.h: Renumber STYLE_PASSAGE and STYLE_NOSURVEY so
that the style constants we want to pass to img are contiguously
numbered.
src/img.h: Remove unnecessary include of "useful.h" in IMG_HOSTED
mode.
doc/TODO.htm: Update.
src/commands.c: Fix ordering of the style masks to reflect swapping
of STYLE_NOSURVEY and STYLE_PASSAGE.
doc/3dformat.htm,doc/TODO.htm,src/img.h: Start on v8 of the 3d format
- the timestamp is stored as seconds since 1970.
doc/3dformat.htm,doc/TODO.htm,src/img.c: Add an explicit flag for
'this is an extended elevation' to 3d v8.
doc/3dformat.htm: Formatting tweaks.