fix benchmark results formatting

bench_results.md

@@ -3,50 +3,66 @@ Processor: Intel i5-5200U (2.2GHz/2.7GHz turbo)
 # bf.py, very naive
 
 ## bench.b
+```
 real    14m8.526s
 user    14m8.542s
 sys     0m0.010s
+```
 
 ## mandel.b
+```
 real    209m11.773s
 user    209m11.755s
 sys     0m0.374s
+```
 
 
 # bf2.py, non-slot
 
 ## bench.b
+```
 real    10m21.137s
 user    10m21.162s
 sys     0m0.010s
+```
 
 ## mandel.b
+```
 real    103m31.439s
 user    103m30.069s
 sys     0m0.813s
+```
 
 
 # bf2.py, slotted
 
 ## bench.b
+```
 real    9m10.573s
 user    9m10.418s
 sys     0m0.127s
+```
 
-# mandel.b
+## mandel.b
+```
 real    93m11.907s
 user    93m10.734s
 sys     0m0.673s
+```
 
 
 # pypy3 bf2.py, slotted
 
 ## bench.b
+```
 real    0m29.793s
 user    0m29.759s
 sys     0m0.033s
+```
 
 ## mandel.b
+```
 real    2m36.409s
 user    2m36.338s
 sys     0m0.063s
+```