copy = (out, line) => {
  vec3.copy(out[0], line[0])
  vec3.copy(out[1], line[1])
  return out
}
Copy the given line into the receiving line.

@param {line3} out - receiving line
@param {line3} line - line to copy
@returns {line3} out
@alias module:modeling/maths/line3.copy