bool_point intersection_point (const Path& p, const bool trace)  Function 
Finds the intersection point, if any, of two linear Paths .
Let bp be the bool_point returned by
this function. bp.pt will contains the
intersection point, if it exists. If not, it will contain
INVALID_POINT . If the intersection point exists and lies on both
of the line segments represented by the Path and p ,
bp.b will be true , otherwise, false .
This function calls Point A(1, 1, 1); Point B(1, 1, 1); Path p0(A, B); Point C(2, 1, 1); Point D(1.75, 0.25, 0.25); Path p1(C, D); bool_point bp = p0.intersection_point(p1); bp.pt.dotlabel("$i$"); bp.pt.show("bp.pt:");  bp.pt: (0.5, 0.5, 0.5)
