add arithmetic operator to Point3D; fix some little bugs

Signed-off-by: anti-freak <antifreak2011@gmail.com>
add floating type specialization to Point(3D); add intersects(); add another contains function

Signed-off-by: anti-freak <antifreak2011@gmail.com>
fix last commit

Signed-off-by: anti-freak <antifreak2011@gmail.com>