Reworked how filesystem-level config is stored

Now, instead of storing a single contiguous block of config data, config
is stored as tagged metadata like any other attribute.

This allows more flexibility towards adding/removing config in the
future, without cluttering up the config with deprecated entries (see
ATA's "IDENTIFY DEVICE" response).

Most of the config entries are single leb128 limits on various integer
types, with the exception of the magic string and version (major/minor
pair).

---

Note this also includes some semantic changes to the config:

- Limits are stored as size-1. This avoid issues with integer overflow
  at extreme ranges.

  This was also adopted for block size (block limit) and block count
  (disk limit). This deviation between on-disk config and user-facing
  config risks confusion, but allows the potential for the full 2^31 range
  for these values.

- The default cksum type, crc32c, has been changed to 0.

  Originally this was 2 to allow the type to map to the crc width for
  crc8, crc16, crc32c, crc64, etc. But dropping this idea and numbering
  checksums as they are implemented simplifies things.

  May come back to this.

- Storing these configs as attributes opens up of the option of on-disk
  defaults when configs are missing.

  I'm being a bit conservative with this one, as it's not clear to me if
  we should prefer default configs (less code/storage, risk of untested
  config parsing) or prefer explicit on-disk configs.

  Currently the following have defaults since they seem the most obvious
  to me:

  - cksum type  => defaults to crc32c
  - redund type => defaults to parity (TODO, should this default to
    no redund?)
  - utag_limit  => defaults to 0x7f (no special tag decoding)
  - uattr_limit => defaults to block_limit (implicit)

lfs.h

@@ -75,11 +75,12 @@ typedef int32_t  lfsr_sdid_t;
 #define LFS_FILE_MAX 2147483647
 #endif
 
-// Maximum size of custom attributes in bytes, may be redefined, but there is
-// no real benefit to using a smaller LFS_ATTR_MAX. Limited to <= 1022.
-#ifndef LFS_ATTR_MAX
-#define LFS_ATTR_MAX 1022
-#endif
+// TODO rm me
+//// Maximum size of custom attributes in bytes, may be redefined, but there is
+//// no real benefit to using a smaller LFS_ATTR_MAX. Limited to <= 1022.
+//#ifndef LFS_ATTR_MAX
+//#define LFS_ATTR_MAX 1022
+//#endif
 
 // Possible error codes, these are negative to allow
 // valid positive return values
@@ -261,23 +262,24 @@ struct lfs_config {
     // larger names except the size of the info struct which is controlled by
     // the LFS_NAME_MAX define. Defaults to LFS_NAME_MAX when zero. Stored in
     // superblock and must be respected by other littlefs drivers.
-    lfs_size_t name_max;
+    lfs_size_t name_limit;
 
     // Optional upper limit on files in bytes. No downside for larger files
     // but must be <= LFS_FILE_MAX. Defaults to LFS_FILE_MAX when zero. Stored
     // in superblock and must be respected by other littlefs drivers.
-    lfs_size_t file_max;
+    lfs_size_t size_limit;
 
-    // Optional upper limit on custom attributes in bytes. No downside for
-    // larger attributes size but must be <= LFS_ATTR_MAX. Defaults to
-    // LFS_ATTR_MAX when zero.
-    lfs_size_t attr_max;
-
-    // Optional upper limit on total space given to metadata pairs in bytes. On
-    // devices with large blocks (e.g. 128kB) setting this to a low size (2-8kB)
-    // can help bound the metadata compaction time. Must be <= block_size.
-    // Defaults to block_size when zero.
-    lfs_size_t metadata_max;
+// TODO rm me
+//    // Optional upper limit on custom attributes in bytes. No downside for
+//    // larger attributes size but must be <= LFS_ATTR_MAX. Defaults to
+//    // LFS_ATTR_MAX when zero.
+//    lfs_size_t attr_max;
+//
+//    // Optional upper limit on total space given to metadata pairs in bytes. On
+//    // devices with large blocks (e.g. 128kB) setting this to a low size (2-8kB)
+//    // can help bound the metadata compaction time. Must be <= block_size.
+//    // Defaults to block_size when zero.
+//    lfs_size_t metadata_max;
 };
 
 // File info structure
@@ -505,9 +507,8 @@ typedef struct lfs {
     } lookahead;
 
     const struct lfs_config *cfg;
-    lfs_size_t name_max;
-    lfs_size_t file_max;
-    lfs_size_t attr_max;
+    lfs_size_t name_limit;
+    lfs_off_t size_limit;
 
     // begin lfsr things
     lfsr_grm_t grm;