More understandable documentation for line class

[RobotJente]

The documentation of the forward and general intersect classes is convoluted. This can be fixed by making a Halfline class, since currently the forward intersect is the only method that treats a line as a half line, which does not make sense, both in design and mathematically. Additionally, I'm pretty sure the current documentation for forwardIntersect is incomplete, as it is unclear what a direction vector is, and what the point b is.

Additionally, the documentation for the "general intersect" needs to be shorter. Less words, and more precise. Use math if needed. See the updated forwardIntersect documentation for inspiration