rre: add a sys:system word

FossilOrigin-Name: 72327d3b0cc6574bc791de4b5bb6ecbd27e0b41cf198e110a19e42e1f967dfbb

interfaces/rre.c

@@ -339,6 +339,7 @@ void execute(int cell) {
                     stack_push(string_inject(sys_argv[a + 2], b));
                     break;
         case -6200: ngaGopherUnit(); break;
+        case -8000: system(string_extract(stack_pop())); break;
         default:   printf("Invalid instruction!\n");
                    printf("At %d, opcode %d\n", ip, opcode);
                    exit(1);

interfaces/rre.forth

@@ -73,6 +73,12 @@ Returns:
 :sys:argv (n-s) s:empty swap `-6101 ;
 ~~~
 
+# System Interaction
+
+~~~
+:sys:system (s-) `-8000 ;
+~~~
+
 ---------------------------------------------------------------
 
 # File I/O

literate/Rx.md

@@ -1,7 +1,7 @@
     ____  _   _
     || \\ \\ //
     ||_//  )x(
-    || \\ // \\ 2017.11
+    || \\ // \\ 2017.12
     a minimalist forth for nga
 
 *Rx* (*retro experimental*) is a minimal Forth implementation for the
@@ -55,7 +55,7 @@ r 9999
 d 1536
 
 : Version
-d 201711
+d 201712
 ~~~
 
 Both of these are pointers. `Dictionary` points to the most recent