Renamed traversal -> trv

- test_traversal -> test_trvs
- lfs3_traversal_t -> lfs3_trv_t
- lfs3_btraversal_t -> lfs3_btrv_t
- t -> trv
- bt -> btrv
- lfs3_traversal_* -> lfs3_trv_*
- lfs3_btraversal_* -> lfs3_btrv_*

The traversal type is becoming one of the more fundamental types in
littlefs, and if DIR and REG both get shortened names, it makes sense
for TRV to have one as well.

This also removes the temptation to use t for traversals, which is
probably an even worse name.

---

Note that lfs3_btree_traverse, lfs3_mtree_traverse, etc, remain
unaffected. This may change in the future, but it's interesting to note
that verbs seem to need much less typing than nouns.

lfs3.h

@@ -108,7 +108,7 @@ enum lfs3_type {
     // internally used types, don't use these
     LFS3_type_BOOKMARK   = 4,  // Directory bookmark
     LFS3_type_ORPHAN     = 5,  // An orphaned stickynote
-    LFS3_type_TRAVERSAL  = 6,  // An open traversal object
+    LFS3_type_TRV        = 6,  // An open traversal object
 };
 
 // File open flags
@@ -757,20 +757,20 @@ typedef struct lfs3_dir {
     lfs3_off_t pos;
 } lfs3_dir_t;
 
-typedef struct lfs3_btraversal {
+typedef struct lfs3_btrv {
     lfs3_bid_t bid;
     const lfs3_rbyd_t *branch;
     lfs3_srid_t rid;
     lfs3_rbyd_t rbyd;
-} lfs3_btraversal_t;
+} lfs3_btrv_t;
 
 // littlefs traversal type
-typedef struct lfs3_traversal {
+typedef struct lfs3_trv {
     // mdir/bshrub/btree state, this also includes our traversal
     // state machine
     lfs3_bshrub_t b;
     // opened file state
-    lfs3_handle_t *ht;
+    lfs3_handle_t *htrv;
     union {
         // cycle detection state, only valid when traversing the mroot chain
         struct {
@@ -779,16 +779,16 @@ typedef struct lfs3_traversal {
             uint8_t power;
         } mtortoise;
         // btree traversal state
-        lfs3_btraversal_t bt;
+        lfs3_btrv_t btrv;
         // graft traversal state
-        lfs3_size_t gt;
+        lfs3_size_t gtrv;
     } u;
 
     // recalculate gcksum when traversing with ckmeta
     uint32_t gcksum;
-    // pending blocks, only used in lfs3_traversal_read
+    // pending blocks, only used in lfs3_trv_read
     lfs3_sblock_t blocks[2];
-} lfs3_traversal_t;
+} lfs3_trv_t;
 
 // grm encoding:
 // .- -+- -+- -+- -+- -.  mids:  2 leb128s  <=2x5 bytes
@@ -886,7 +886,7 @@ typedef struct lfs3 {
     // optional incremental gc state
     #ifdef LFS3_GC
     struct {
-        lfs3_traversal_t t;
+        lfs3_trv_t trv;
     } gc;
     #endif
 } lfs3_t;
@@ -1241,13 +1241,13 @@ int lfs3_dir_rewind(lfs3_t *lfs3, lfs3_dir_t *dir);
 // the filesystem.
 //
 // Returns a negative error code on failure.
-int lfs3_traversal_open(lfs3_t *lfs3, lfs3_traversal_t *t, uint32_t flags);
+int lfs3_trv_open(lfs3_t *lfs3, lfs3_trv_t *trv, uint32_t flags);
 
 // Close a traversal
 //
 // Releases any allocated resources.
 // Returns a negative error code on failure.
-int lfs3_traversal_close(lfs3_t *lfs3, lfs3_traversal_t *t);
+int lfs3_trv_close(lfs3_t *lfs3, lfs3_trv_t *trv);
 
 // Progress the traversal and read an entry
 //
@@ -1255,13 +1255,13 @@ int lfs3_traversal_close(lfs3_t *lfs3, lfs3_traversal_t *t);
 //
 // Returns 0 on success, LFS3_ERR_NOENT at the end of traversal, or a
 // negative error code on failure.
-int lfs3_traversal_read(lfs3_t *lfs3, lfs3_traversal_t *t,
+int lfs3_trv_read(lfs3_t *lfs3, lfs3_trv_t *trv,
         struct lfs3_tinfo *tinfo);
 
 // Reset the traversal
 //
 // Returns a negative error code on failure.
-int lfs3_traversal_rewind(lfs3_t *lfs3, lfs3_traversal_t *t);
+int lfs3_trv_rewind(lfs3_t *lfs3, lfs3_trv_t *trv);
 
 
 /// Filesystem-level filesystem operations