SWHID v2: determine binary-to-text encoding for checksum part

The binary-to-text encoding for SWHID v1 is hex. We need to determine what the encoding for v2 will be.

The main problem with hex is length, which is already a limiting factor for v1 when SWHIDs need to be written in places where place does matter (e.g., scientific publications). The problem is going to be much more significant with SWHID v2, where the checksum size will increase.

This task tracks the need of deciding what to use. Some preliminary options are:

• hex
• base58
• base64
• ascii85

A useful comparison table is available on wikipedia.

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Migrated from T3316 (view on Phabricator)