comment parsing, marbles pass through spaces in comments. fix crash on division by zero

programs/adder.mbl

@@ -0,0 +1,28 @@
+(print sum of 123 and 45)
+
+  o
+  > 123   B
+ vo      A-+
+  > 45    B|
+  o      --+
+  >      *  B
+         o
+   (check if 0)
+     o   1
+v  < B=- 0
+ v   o * D- (div/10)
+v       B *  <
+
+v> * 1    o  ^
+ F -R0  * 4 B
+*| # <  -A8 v
+ |      # <
+#|
+ -|            v   <
+  |         *-|o
+  F           +B * ^
+ #<         \F----
+(ascii digit s)
+(printed in)*-|
+(reverse)    P-
+            B