Include type in panic message (#50)

Previous this message looked like:

    Can't handle <nil>

After this change:

    Can't handle type interface {} with value <nil>

fuzz.go

@@ -358,7 +358,7 @@ func (fc *fuzzerContext) doFuzz(v reflect.Value, flags uint64) {
 	case reflect.Interface:
 		fallthrough
 	default:
-		panic(fmt.Sprintf("Can't handle %#v", v.Interface()))
+		panic(fmt.Sprintf("Can't handle type %v with value %#v", v.Type(), v.Interface()))
 	}
 }