Declare a byte version of the data

Declare a byte version of the data field.  This fixes Issue #40
diff --git a/include/cn-cbor/cn-cbor.h b/include/cn-cbor/cn-cbor.h
index 2973581..bf71af8 100644
--- a/include/cn-cbor/cn-cbor.h
+++ b/include/cn-cbor/cn-cbor.h
@@ -81,7 +81,9 @@
   /** Data associated with the value; different branches of the union are
       used depending on the `type` field. */
   union {
-    /** CN_CBOR_BYTES, CN_CBOR_TEXT */
+    /** CN_CBOR_BYTES */
+    const uint8_t* bytes;
+    /** CN_CBOR_TEXT */
     const char* str;
     /** CN_CBOR_INT */
     long sint;