LTYPE: struct members according to R14.

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

Signed-off-by: bert <bert.timmerman@xs4all.nl>
LTYPE: updated Doxygen comments for stuct members.

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