Implement a growing insertion.

include/sprs.h

@@ -95,6 +95,16 @@ void sprs_free(sprs* sprs);
  * @param data the value to store.
  */
 void sprs_put(sprs* sprs, size_t index, void* data);
+/**
+ * Stores a value in the sparse set under a given index.
+ * If the capacity of the sparse set is smaller than the given index,
+ * this grows the sparse set by doubling its size.
+ * @param sprs the sparse set into which to store the value.
+ * @param index the index at which to store the value.
+ * @param data the value to store.
+ * @return LIBDS_SUCCESS if all goes well, or LIBDS_MALLOC if the growing failed.
+ */
+libds_result sprs_put_grow(sprs* sprs, size_t index, void* data);
 /**
  * Checks if the sparse set contains data under a given index.
  * @param sprs the sparse set to check.