skip existing examples on generation (#616)

Author: NouemanKHAL

extract-code-blocks.awk

@@ -49,6 +49,10 @@ function camel(value) {
         }
         system("mkdir -p " output "/" tag);
         out_file=output "/" tag "/" operation_id ".pybeta";
+        if (system("[ -f " out_file " ]") == 0) {
+            printf "skipped: "
+            in_code_block = 0;
+        }
         print out_file;
     } else {
         print "Can't parse " FILENAME > "/dev/stderr"