Merge pull request #18 from ray-project/fix

Fixed extern C declaration (found by Mehrdad)

Author: robertnishihara

python/src/pynumbuf/adapters/python.cc

@@ -8,9 +8,13 @@ using namespace arrow;
 
 int32_t MAX_RECURSION_DEPTH = 100;
 
+extern "C" {
+
 extern PyObject* numbuf_serialize_callback;
 extern PyObject* numbuf_deserialize_callback;
 
+}
+
 namespace numbuf {
 
 Status get_value(ArrayPtr arr, int32_t index, int32_t type, PyObject* base, PyObject** result) {