Restructure code: split features into separate files

aux/valval.typ

@@ -0,0 +1,8 @@
+// valval - the value validator (tm)
+
+// panics if value is not in the allowed array
+#let panicOnInvalid(value, allowed) = {
+  if allowed.find(x => x == value) == none {
+    panic("Value " + value + " is not in " + allowed.join(", "))
+  }
+}