important - change to AC3D file format

[Andy]

The next release increments the file format version and makes it 'c'.

This means that the first line of a new .ac file will change from "AC3Db" to AC3Dc". Older files are still compatible.

Objects now have an (optional) crease angle attribute e.g.

crease 45.0

This indicates that if the angles between two joined surfaces is more than 45 degrees, the edges between the surfaces will be drawn with a crease.

Valid crease angles are 0.0 to 180.0 degrees.

Setting a surface to flat-shaded forces it always to be drawn flat.

The default crease-angle in AC3D is currently 45 degrees.

Comments welcome.

[Andy]

Since incrementing the AC3D file version in the header causes older versions of AC3D to reject the file AND the fact that adding just the crease line doesn't force rejection (older versions will simply print 'ignoring crease') - I have decided to not increment the file version.

This means that new files will still have AC3Db as the header, and objects may have the crease attribute.

If you have written an AC3D file loader correctly, this should not cause problems.

Andy