sample-code: proper type annotations on HEX_LUT, add FIXME for min and max

sample-code/math.cl

@@ -1,9 +1,15 @@
 //! Useful math functions
 
+// FIXME:
+// These two functions shouldn't actually be polymorphic, but
+// the AST interpreter doesn't know about type annotations
+// or operator overloading.
+#[generic("T")]
 pub fn max(a: T, b: T) -> T {
     (if a < b { b } else { a })
 }
 
+#[generic("T")]
 pub fn min(a: T, b: T) -> T {
     (if a > b { b } else { a })
 }