Base-16 support

[John-LittleBearLabs]

Fixes #45

Also, changed how unsupported multibases are reported. No more asserting/crashing.

Simply not crashing, though, causes it to repoint to about:blank#blocked which is just a blank page so the only clue you have as to what went wrong is the confusing & misleading location bar text.

I have access to limited error reporting when canonicalizing URLs, so I decided to "successfully" canonicalize it into an identity CID ipfs:// URL (conceptually similar to a data:// URL) that points to an error message.

[codecov]

Codecov Report

Patch coverage: 57.14% and project coverage change: +0.95% 🎉

Comparison is base (479894a) 52.45% compared to head (7e4b466) 53.40%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #46      +/-   ##
==========================================
+ Coverage   52.45%   53.40%   +0.95%     
==========================================
  Files          48       50       +2     
  Lines        2381     2479      +98     
==========================================
+ Hits         1249     1324      +75     
- Misses       1132     1155      +23     

Files Changed	Coverage Δ
library/src/libp2p/crypto/hasher.cc	57.14% <ø> (ø)
.../src/libp2p/multi/multibase_codec/codecs/base16.cc	43.03% <43.03%> (ø)
...brary/src/libp2p/multi/content_identifier_codec.cc	46.91% <46.66%> (+3.04%)	⬆️
library/src/ipfs_client/identity_cid.cc	66.66% <66.66%> (ø)
library/src/ipfs_client/block_storage.cc	57.14% <100.00%> (+0.85%)	⬆️
library/src/ipfs_client/dag_block.cc	57.34% <100.00%> (+0.91%)	⬆️
library/src/ipfs_client/gateways.cc	46.42% <100.00%> (ø)
...bp2p/multi/multibase_codec/multibase_codec_impl.cc	52.27% <100.00%> (+13.49%)	⬆️

... and 9 files with indirect coverage changes

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