Canonicalize UCANs by default

[expede]

IMO (feel free to disagree), following Postel's Law, UCAN libraries should be rigid in what they produce, and liberal in what they accept. To this end, it would be amazing if this library produced canonicalized UCANs compatible with ucan-ipld.

This gets us a few things:

• Slick tooling (over time)
• Storage savings form content addressing / deduplication / binary data
• Convert UCANs into arbitrary formats (e.g. machine friendly, PB, CBOR, Arrow, etc)

We will still need to read in arbitrary JWTs, but the more canonicalized UCANs that exist, the better a world we live in 😉

[matheus23]

Solving this issue would be a superset of #73 I think.