Corner t-joint for square poles

Simple, fully parameterized, easy to configure corner t-joint for square poles.

Simply specify width and depth of the poles and the screw hole diameter. You can specify the thickness of the walls too. With tear=true/false and countersunk=true/false it is possible to specify the type and shape of the screw holes. It is also possible to specify two angles (alpha and beta), which control the angles of the screw holes (only makes a difference when you choose the teardrop shape of the screw holes)