fuzzing: Fuzz different print methods

This is achieved by encoding the type of function used in the first two
bytes.

First byte:
b: buffered

Second byte:
f: formatted

fuzzing/inputs/test6

@@ -1,4 +1,4 @@
-<!DOCTYPE html>
+bf<!DOCTYPE html>
     <html>
     <head>
       <meta name="viewport" content="width=device-width, initial-scale=1">
@@ -13,4 +13,4 @@
         <p>Application Error</p>
       </iframe>
     </body>
-    </html>
+    </html>