primitive compounds for OpenSCAD, partial hollow

I always try to keep my code lean.
This is why I started to create a library for more complex compounds.
Today it contains:
rounding
drill_cone_head
pyramid
tri_angle
hollow_sphere
hollow_cylinder
rounded_cylinder
sloped_cylinder
hollow_cube
rounded_cube
hollow_rounded_cube

Last edit history:
added sloped_cylinder
added rounded_cylinder

Improved Rendering time and preview of hollow items.
Added rounding to round inner and outer corners.
Added drill_cone_head
Added dimensi