py: Rename byte_code to bytecode everywhere.

bytecode is the more widely used.  See issue #590.
diff --git a/py/mpconfig.h b/py/mpconfig.h
index 119859a..f840414 100644
--- a/py/mpconfig.h
+++ b/py/mpconfig.h
@@ -100,7 +100,7 @@
 
 // Whether to build functions that print debugging info:
 //   mp_token_show
-//   mp_byte_code_print
+//   mp_bytecode_print
 //   mp_parse_node_print
 #ifndef MICROPY_DEBUG_PRINTERS
 #define MICROPY_DEBUG_PRINTERS (0)