Add SoftWare Heritage persistent IDentifiers

See
https://docs.softwareheritage.org/devel/swh-model/persistent-identifiers.html
for the technical details of that spec.

Software Heritage has done a superb job promoting content addressing in
general, and their identifier scheme (SWHIDs, for short) in particular.
By supporting them in CIDs / IPLD, I hope the IPFS ecosystem can align
itself with that effort.

Per the linked documentation, SWHIDs have their own nested grammar and
versioning scheme. I have taken the version 1 core identifier grammar,
unrolled it, and replaced `:` with `-` per the guidelines on separators,
with the result being these 5 rows.

Also note that some of those schemes coincide with certain forms of
`git-raw`, already in this table. However, adding them here is not
redundant, because the deserialization direction. While a git-raw CID
may legally point to any sort of git object, the relevant SWHIDs specify
in the identifier what sort of git object is expected, and if it points
to a different type of valid git object, deserialization fails. That
means there is no way to losslessly convert a git-coinciding SWHID into
a git-raw CID.

table.csv

@@ -110,6 +110,11 @@ ws,                             multiaddr,      0x01dd,
 wss,                            multiaddr,      0x01de,
 p2p-websocket-star,             multiaddr,      0x01df,
 http,                           multiaddr,      0x01e0,
+swhid-v1-snp,                   ipld,           0x01f0,         SoftWare Heritage persistent IDentifier version 1 snapshot
+swhid-v1-rel,                   ipld,           0x01f1,         SoftWare Heritage persistent IDentifier version 1 release
+swhid-v1-rev,                   ipld,           0x01f2,         SoftWare Heritage persistent IDentifier version 1 revision
+swhid-v1-dir,                   ipld,           0x01f3,         SoftWare Heritage persistent IDentifier version 1 directory
+swhid-v1-cnt,                   ipld,           0x01f4,         SoftWare Heritage persistent IDentifier version 1 content
 json,                           serialization,  0x0200,         JSON (UTF-8-encoded)
 messagepack,                    serialization,  0x0201,         MessagePack
 libp2p-peer-record,             libp2p,         0x0301,         libp2p peer record type