port/merge Eurecom APER support from OPENAIRMME

Eurecom has developed APER support for asn1c as part of the OPENAIRMME
softare (a LTE MME).  This is too important to let it bit-rout out
of asn1c.  Let's forward-port and merge it.
diff --git a/skeletons/NULL.h b/skeletons/NULL.h
index 131e775..90784d8 100644
--- a/skeletons/NULL.h
+++ b/skeletons/NULL.h
@@ -25,6 +25,8 @@
 xer_type_encoder_f NULL_encode_xer;
 per_type_decoder_f NULL_decode_uper;
 per_type_encoder_f NULL_encode_uper;
+per_type_decoder_f NULL_decode_aper;
+per_type_encoder_f NULL_encode_aper;
 
 #ifdef __cplusplus
 }