Make LineSegment3d documentation more explicit
Make LineSegment3d documentation more explicit

- Use comments to show output of functions instead of using '=='; makes
it more obvious what is example code and what is the result of that code
- Rename 'lineSegment' to 'exampleLineSegment' to make it more clear
that it is being reused in function documentation examples
- Reorder endpoint functions ('endpoints' is slightly more complex than
'startPoint' and 'endPoint')

opensolid/geometry