Number serialization options

[cyberphone]

Related: json-schema-org/json-schema-vocabularies#45

In many places including in IETF standards like JOSE, BigIntegers are represented not only as JSON Strings, but as specifically encoded such:
https://tools.ietf.org/html/rfc7518#section-6.3.1

This also permits hassle-free, cross-platform JSON messaging since IEEE-754 remains an issue in JavaScript.

In fact, even an int64 fails (loses data) using ECMAScript's JSON.parse() since IEEE-754 double precision only provides 53 bits of precision.

[handrews]

This is a duplicate of json-schema-org/json-schema-vocabularies#45. We don't need any convincing on the utility of numbers encoded as strings. As I have stated many times, we just need someone knowledgeable to step up and write a PR. If you are willing to do that, please make a note in json-schema-org/json-schema-vocabularies#45.