feat(lsm): store data files in nested subdirectories

lsm/include/lsm/store.h

@@ -7,6 +7,8 @@
 #include "lsm.h"
 #include "lsm/str.h"
 
+#define LSM_STORE_DATA_LEVELS 3
+
 /**
  * A handle referencing an entry inside a store. Read/write operations from/to
  * the entry go through this handle.
@@ -155,7 +157,7 @@ lsm_error lsm_store_open_read(lsm_entry_handle **out, lsm_store *store,
  * @param key key to search
  */
 lsm_error lsm_store_open_write(lsm_entry_handle **out, lsm_store *store,
-                              const lsm_str *key);
+                               const lsm_str *key);
 
 /**
  * Close an open entry handle.