add rack-mount build directory, add stack mount stls, and some general fixes

helper/halfspace.scad

@@ -1,10 +1,7 @@
-
-// Wake up sheeple. Halfspaces are just really BIG cubes!
-include <./math.scad>
 include <./common.scad>
 
 module halfspace(vpos, p) {
-    // TODO: clean up
+
     ref = [0,0,-1];
 
     if (cross(ref, vpos) == [0,0,0]) {
@@ -17,4 +14,12 @@ module halfspace(vpos, p) {
         translate(v = [0, 0, -inf/2])
         cube(size = [inf, inf, inf], center = true);
     }
+
+    module align(a,b) {
+        rot_axis = cross(a,b);
+        angle = acos(a*b/(norm(a)*norm(b)));
+
+        rotate(v=rot_axis, a=angle)
+        children(0);
+    }
 }