EIP4361 parser

The goal is to build a parser using apg-js. This could be done with:

const apgApi = require("apg-js/src/apg-api/api");

const GRAMMAR = ` ... `;
const api = new apgAPI(GRAMMAR);
api.generate();

const grammarObj = api.toObject();

Unfortunately, apgApi requires Buffer which isn't in the browser.

So, we build the grammar from scratch:

cd node_modules/apg-js
npm run apg -- -i ../../EIP4361/grammar.abnf -o ../../src/web3/eip4361-grammar.js

and then use

const grammar = new (require('./eip4361-grammar.js'))();

Sadly, apgLib.parser().parse() also requires Buffer.

Regardless, we're continuing to use the generated eip4361-grammar.js file.