src/dump3d.c: Show only 2 decimal places on coordinates and passage
dimensions.
src/img.c: Revert to putting a human readable timestamp string in
v7 and older files.
src/dump3d.c,src/netskel.c: The fBinary parameter of img_open_write()
has been unused for years, so stop passing fTrue.
configure.ac,doc/3dformat-old.htm: Split off a copy of the current
3dformat document - v8 will feature significant changes, so it will
be clearer to document it separately.
src/: Track the data style of each leg, and pass it in to img - it's
not yet stored in the .3d file, but now it is easily available so it
can be.
src/dump3d.c: Report if the file is an extended elevation.
NEWS,src/dump3d.c,src/img.h: Drop img_FLAG_NOSURVEY - it's redundant
now we're going to store the style of each leg, and it hasn't yet
been in a release.
src/img.h: Add comments for the lists of "Leg flags" and "Station
flags".
src/extend.c,src/img.c,src/img.h: Repurpose the long unused fBinary
parameter to img_open_write() as a flags parameter, and add
img_FFLAG_EXTENDED to specify that this is an extended elevation,
in place of appending " (extended)" to the title.  Internally we
still append this to the title (and remove it upon reading), but in
the 3d v8 format, the flags will be stored explicitly in the file.
src/img.h: Just make fRead always int, eliminating IMG_HOSTED
conditional.