Detect CID in Subdomains

[lidel]

(Parent issues: ipfs/ipfs-companion#526, ipfs/in-web-browsers#89)

• Do a quick check via regexp and then do proper validation on positive matches, just like we do for URLs and Paths:

  In these cases, the CID will always be in a zone named ipfs (or ipns), e.g. http://bafkreigh2akiscaildcqabsyg3dfr6chu3fgpregiymsck7e7aqa4s52zy.ipfs.dweb.link, so a regexp could look something like ^b[^.]{42,}\.ipfs\. (42 being a made-up minimum length for a base32 CID).
  – Detect CID in subdomains ipfs/ipfs-companion#526 (comment)

• We probably want to add it under isIPFS.subdomain (ipns or ipfs), isIPFS.ipfsSubdomain and isIPFS.ipnsSubdomain.
  • Also, make it clear in docs that it is not related to dnslink or ipns.