SPLINE: added dxf_spline_read().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
HELIX: added more code to dxf_helix_read().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
SPLINE: added Doxygen comments.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
HELIX: let dxf_helix_write() write control points, fit points,
weight values, tangents and tolerances.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
SPLINE: added dxf_spline_write().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
HELIX: additions to dxf_helix_read() and dxf_helix_write().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
VERTEX: use DxfFile and additions.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
3DFACE: removed dxf_3dface_write_lowlevel().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
3DFACE: corrections in writing order.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
3DSOLID: removed dxf_3dsolid_write_lowlevel().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
global.h: added the default visibility.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
3DFACE: initialise to default linetype scale and visibility.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
3DSOLID: corrections in writing order.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
3DFACE: read linetype scale and visibility.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
3DSOLID: read linetype scale and visibility.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
ARC: removed dxf_arc_write_lowlevel().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
ARC: corrections in writing order.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
ATTDEF: removed dxf_attdef_write_lowlevel().

Signed-off-by: bert <bert.timmerman@xs4all.nl>
ATTDEF: corrections in writing order.

Signed-off-by: bert <bert.timmerman@xs4all.nl>
ARC: corrections in writing order.

Signed-off-by: bert <bert.timmerman@xs4all.nl>