add some prep files

helper/halfspace.scad

@@ -0,0 +1,2 @@
+// TODO
+// probably want to get rotations first

helper/math.scad

@@ -1,4 +1,4 @@
-
+// TODO remove/rename this file
 /* Example usage:
 for (i=mirror4XY(midpoint=[0,0,0], offsetX=90, offsetY=90)) {
     translate(v=i)

helper/rotation.scad

@@ -0,0 +1,3 @@
+// TODO
+
+// eg transformation to rotate vector a to vector b, etc

rack/derivedConfig.scad

@@ -0,0 +1,4 @@
+// Config file for derived variables. These variables are calculated from profile variables and are used by
+// multiple components.
+
+// TODO