py: Move to guarded includes, everywhere in py/ core.

Addresses issue #1022.
diff --git a/py/emitcommon.c b/py/emitcommon.c
index e199bc6..4d90983 100644
--- a/py/emitcommon.c
+++ b/py/emitcommon.c
@@ -28,16 +28,7 @@
 #include <stdint.h>
 #include <assert.h>
 
-#include "mpconfig.h"
-#include "misc.h"
-#include "qstr.h"
-#include "lexer.h"
-#include "parse.h"
-#include "runtime0.h"
-#include "obj.h"
-#include "emitglue.h"
-#include "scope.h"
-#include "emit.h"
+#include "py/emit.h"
 
 #define EMIT(fun, ...) (emit_method_table->fun(emit, __VA_ARGS__))