Enabled SDL_image's support for PNG and TIFF files and improved the

AssetManager with a hashing function, a linked list structure to store
the hashes as well as a reference counter to support multiple users
sharing the same asset.

include/reusable_ids.h

@@ -4,9 +4,19 @@
 #include <stddef.h>
 #include <stdint.h>
 
+#ifdef __cplusplus
+extern "C" {
+#endif // !__cplusplus
+
+#define INVALID_ID -1
+
 typedef int32_t ObjectID;
 typedef int32_t AssetID;
 
 int32_t reuse_id(int32_t *ids, size_t count);
 
+#ifdef __cplusplus
+}
+#endif // !__cplusplus
+
 #endif // !REUSABLE_IDS_H