Changes the cn_cbor_context macros to use const

include/cn-cbor/cn-cbor.h

diff --git a/include/cn-cbor/cn-cbor.h b/include/cn-cbor/cn-cbor.h
index 4e8dfb8..e59ce44 100644
--- a/include/cn-cbor/cn-cbor.h
+++ b/include/cn-cbor/cn-cbor.h
@@ -250,10 +250,10 @@
 
 /** When USE_CBOR_CONTEXT is defined, many functions take an extra `context`
  * parameter */
-#define CBOR_CONTEXT , cn_cbor_context* context
+#define CBOR_CONTEXT , const cn_cbor_context* context
 /** When USE_CBOR_CONTEXT is defined, some functions take an extra `context`
  * parameter at the beginning */
-#define CBOR_CONTEXT_COMMA cn_cbor_context *context,
+#define CBOR_CONTEXT_COMMA const cn_cbor_context *context,
 
 #else