Separated type/struct fields in dir entries

The separation of data-structure vs entry type has been implicit for a
while now, and even taken advantage of to simplify the traverse logic.

Explicitely separating the data-struct and entry types allows us to
introduce new data structures (inlined files).

lfs.h

@@ -74,9 +74,15 @@ enum lfs_error {
 
 // File types
 enum lfs_type {
-    LFS_TYPE_REG        = 0x11,
-    LFS_TYPE_DIR        = 0x22,
-    LFS_TYPE_SUPERBLOCK = 0x2e,
+    // file type
+    LFS_TYPE_REG        = 0x01,
+    LFS_TYPE_DIR        = 0x02,
+    LFS_TYPE_SUPERBLOCK = 0x0e,
+
+    // on disk structure
+    LFS_STRUCT_CTZ      = 0x10,
+    LFS_STRUCT_DIR      = 0x20,
+    LFS_STRUCT_MOVED    = 0x80,
 };
 
 // File open flags