Generate JSON schema definitions for web clients

[silverjam]

To aide in building various web clients, generate JSON schema definitions to parse the output of sbp2json. This allows web clients (like the drive demo UI) to dispatch on the msg_type field in a JSON dictionary and build a fully native object using the JSON fields that are present.

For example, in JavaScript, something like this would be possible:

import { Convert, MsgVelNED} from "./SbpModule.ts";

const json = getJsonBlob();

if (json['msg_type'] === 529) {
    const msgVelNED = Convert.toMsgVelNED(json);
    // ... do stuff with msgVelNED
}

[denniszollo]

A few very minor things, but very cool. We are now web 2.0 compatible.

[denniszollo]

Can you add your note on the PR about the schema and how to use it to the javascript readme here: https://github.com/swift-nav/libsbp/blob/master/javascript/README.md too ?

[denniszollo]

sweet!

[silverjam]

merging, failure was an (errant) performance regression in python