Use label features and entry points for examples

examples/memory-print.asm

@@ -1,5 +1,9 @@
 ;;; memory-print: An example program that features a subroutine for
 ;;; printing a memory buffer, of any length, as characters.
+
+  ;; Setup label for entrypoint
+  global main
+main:
   ;; Allocate a buffer of 3 characters
   malloc.byte 3
   mov.word 0