s3d_push_line - push line
       #include <s3d.h>
       int s3d_push_line(int object, uint32_t v1, uint32_t v2,
                         uint32_t material);
       Push one line on the line stack of the object. It takes 2
       vertex-index-no, and one material material-index-no. as argument. If
       you have a lot of lines to push, use s3d_push_lines()
       Simon Wunderlich
           Author of s3d