Externalise Erlang Term things (_revs, replication _ids)

@nolanlawson:
>Prior discussion in Pouch: pouchdb/pouchdb#4642

@davisp:
>I just remembered that I wrote a Python JSON canonicalizer a long time ago. The basics are: sort keys when serializing, no added whitespace, strings are Unicode NFD normalized encoded in UTF-8, and floats are serialized using dtoa.c (or similarly compatible code, ie, 1.1 is printed as 1.1, not as 1.100000000000000088817842).
>
>For strings I wonder if it'd be better to requiring anything that's non-ascii to be encoded using the \u escape sequences.
>
>I should probably add a link to the thing: https://github.com/davisp/jsonical

@nolanlawson:
> Yeah in JS a popular one is: https://github.com/substack/json-stable-stringify

We fixed some of this with a recent CVE, but it doesn't address the original request.

Start by reading the prior PouchDB discussion linked in the issue and comparing it with the referenced jsonical and json-stable-stringify approaches. The issue does not name files, tests, or a precise acceptance criterion; done would require agreeing on and implementing the original externalization and canonicalization request beyond the CVE fix.

Written by the indexing model from the issue text.