Move type operations to another structure

Every type has free, print, check_constraints, ber_decoder, der_encoder,
xer_decoder, xer_encoder, uper_decoder, uper_encoder and outmost_tag
operations. We move them out to a separate structure asn_TYPE_operation_t.

Combined with previous logic simplification, these operations are based
on ASN.1 basic types, constructed types and string types. So we can
reduce the space occupied by asn_TYPE_descriptor_t variables.
diff --git a/skeletons/BIT_STRING.h b/skeletons/BIT_STRING.h
index d66c88e..ed3d108 100644
--- a/skeletons/BIT_STRING.h
+++ b/skeletons/BIT_STRING.h
@@ -21,6 +21,7 @@
 } BIT_STRING_t;
 
 extern asn_TYPE_descriptor_t asn_DEF_BIT_STRING;
+extern asn_TYPE_operation_t asn_OP_BIT_STRING;
 extern asn_OCTET_STRING_specifics_t asn_SPC_BIT_STRING_specs;
 
 asn_struct_print_f BIT_STRING_print;	/* Human-readable output */