Add CARv2 IndexSorted (#220)

Ref: ipld/ipld#107

table.csv

@@ -116,6 +116,7 @@ json,                           serialization,  0x0200,         permanent, JSON
 messagepack,                    serialization,  0x0201,         draft,     MessagePack
 libp2p-peer-record,             libp2p,         0x0301,         permanent, libp2p peer record type
 libp2p-relay-rsvp,              libp2p,         0x0302,         permanent, libp2p relay reservation voucher
+car-index-sorted,               serialization,  0x0400,         draft,     CARv2 IndexSorted index format
 sha2-256-trunc254-padded,       multihash,      0x1012,         permanent, SHA2-256 with the two most significant bits from the last byte zeroed (as via a mask with 0b00111111) - used for proving trees as in Filecoin
 ripemd-128,                     multihash,      0x1052,         draft,
 ripemd-160,                     multihash,      0x1053,         draft,