Used more subroutines in fib.asm to make code clearer

Looks way more high level but parses down to a very simple bytecode.
However, because of lack of inline code processing, it relies on the
call stack quite heavily.  With inline labels this would be a much
more compact bytecode.

examples/fib.asm

@@ -7,6 +7,9 @@
   ;; Setup entrypoint
   global main
 main:
+  ;; Setup iterator i
+  push.word 1
+  mov.word 2
   ;; Setup initial REG[0] = 1 and REG[1] = 1
   push.word 1
   mov.word 0
@@ -15,19 +18,7 @@ main:
 
   ;; Print REG[0] and REG[1]
 loopback:
-  push.byte '\t'
+  call print_pair
-  print.char
-  push.reg.word 0
-  print.word
-  push.byte '\n'
-  print.char
-
-  push.byte '\t'
-  print.char
-  push.reg.word 1
-  print.word
-  push.byte '\n'
-  print.char
 
   ;;  REG[0] += REG[1]
   push.reg.word 0
@@ -47,3 +38,50 @@ loopback:
   ;; Jump to `#`
   jump.if.byte loopback
   halt
+
+print_pair:
+  push.byte '\t'
+  print.char
+  call print_i
+  push.byte ':'
+  print.char
+  push.byte ' '
+  print.char
+  call print_reg_0
+  push.byte '\n'
+  print.char
+  call increment_i
+  push.byte '\t'
+  print.char
+  call print_i
+  push.byte ':'
+  print.char
+  push.byte ' '
+  print.char
+  call print_reg_1
+  push.byte '\n'
+  print.char
+  call increment_i
+  ret
+
+increment_i:
+  push.reg.word 2
+  push.word 1
+  plus.word
+  mov.word 2
+  ret
+
+print_i:
+  push.reg.word 2
+  print.word
+  ret
+
+print_reg_0:
+  push.reg.word 0
+  print.word
+  ret
+
+print_reg_1:
+  push.reg.word 1
+  print.word
+  ret