Include extern "C" wrapper in headers so they can be used from C++ code

blkmaker_jansson.h

@@ -5,9 +5,17 @@
 
 #include <blktemplate.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif
+
 extern json_t *blktmpl_request_jansson(gbt_capabilities_t extracaps, const char *lpid);
 extern const char *blktmpl_add_jansson(blktemplate_t *, const json_t *, time_t time_rcvd);
 extern json_t *blkmk_submit_jansson(blktemplate_t *, const unsigned char *data, unsigned int dataid, blknonce_t);
 extern json_t *blkmk_submit_foreign_jansson(blktemplate_t *, const unsigned char *data, unsigned int dataid, blknonce_t);
 
+#ifdef __cplusplus
+}
+#endif
+
 #endif