Use label features and entry points for examples

examples/factorial.asm

@@ -1,7 +1,10 @@
-;;; factorai.asm: A program that generates the factorials of each
+;;; factorial.asm: A program that generates the factorials of each
 ;;;  number from 1 to 24 (24!~=UINT64_MAX).  Using the registers to
 ;;;  store `n` and `n!`.
 
+  ;; Setup entrypoint
+  global main
+main:
   ;; Setup initial REG[0] = 1 and REG[1] = 1
   push.word 1
   mov.word 0
@@ -9,7 +12,7 @@
   mov.word 1
 
   ;; Print `REG[0]: REG[1]`
-  ;; Here is the loop back point `#`
+loopback:
   push.byte '\t'
   print.char
   push.reg.word 0
@@ -39,5 +42,5 @@
   push.reg.word 0
   gte.word
   ;; Jump to `#`
-  jump.if.byte 4
+  jump.if.byte loopback
   halt

examples/fib.asm

@@ -3,6 +3,10 @@
 ;;; pairs of fibonacci numbers, we ensure only a finite amount of
 ;;; memory is necessary for this program to function, unlike a pure
 ;;; stack version.
+
+  ;; Setup entrypoint
+  global main
+main:
   ;; Setup initial REG[0] = 1 and REG[1] = 1
   push.word 1
   mov.word 0
@@ -10,7 +14,7 @@
   mov.word 1
 
   ;; Print REG[0] and REG[1]
-  ;; Here is the loop back point `#`
+loopback:
   push.byte '\t'
   print.char
   push.reg.word 0
@@ -41,5 +45,5 @@
   push.reg.word 1
   gte.word
   ;; Jump to `#`
-  jump.if.byte 4
+  jump.if.byte loopback
   halt

examples/instruction-test.asm

@@ -2,6 +2,10 @@
 ;;; order, with proper calling convention.  Used to test lexer and
 ;;; parser but isn't a semantically correct program, but may be run as
 ;;; first instruction is halt (so program will stop immediately).
+
+  ;; setup entrypoint
+  global main
+main:
   halt
   push.byte 1
   push.hword 2

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