Revised .3d file format

[olly@survex.com]

Hi folks,

Survex 0.97 will have a slightly revised .3d file format.  The changes are
needed to allow the leg flags to be stored in the file, and I've also made a
couple of other tweaks - one reduces the size of .3d files (by 10-20%
typically) and the other removes a restriction on station name length.

Survex 0.97 and later will be able to read .3d files produced by older
versions, but not vice versa.  This also means that third party add-ons will
need updating (those which come to mind are Chasm, SpeleoGen, GLCaverot,
and maybe Therion).  If you aren't the author of something like this, this
message needn't concern you.

(Incidentally, is GLCaverot a live project?  It's described as experimental,
and there haven't been any updates for nearly 2 years...)

If you're using the survex img.c and img.h code to read the file, you'll
need to update these files, adjust the calling code a little, and recompile.
If not, you'll need to update your .3d file reading code.

You may also want to update your code to handle legs flagged as "surface"
differently.  For example, extend now ignores surface legs.

It would be good to get everything updated before 0.97 is released, which
I'd like to happen fairly soon.

If you need assistance, let me know.  I'm currently in China, but will be
back in the UK (and more regular email contact) around June 9th.

Cheers,
Olly