Merge-ignore pull request #89 from ipld/prettyprinter

The original idea of this branch was to explore some reusable
components for codecs; maybe to actually get a useful
prettyprinter; and... actually turned a lot into being a bit of
practical discovery about string encoding and escaping.

Some of those goals were partially accomplished, but in general,
this seems better to chalk up as a learning experience.
#89 (comment)
already does a good job of discussing why, and what as learned.

A lot of the reusable codec components stuff has also now
shaken out, just... in other PRs that were written after the learnings
here.  Namely, #101
was able to introduce some tree transformers; and then
#112 demonstrates how those
can compose into a complete codec end to end.
There's still work to go on these, too, but they seem to have already
grabbed the concept of reusable parts I was hoping for here and gotten
farther with it, so.

These diffs are interesting enough I want to keep them referencable
in history.  But I'm merging them with the "-s ours" strategy, so that
the diffs don't actually land any impact on master.  These commits
are for reference only.