Convert to ESM, keep backward compatibility

[davidyuk]

depends on #295

This PR is supported by the Æternity Foundation

We can drop cjs version in the next major version of calldata 🤔

Motivation:

• react-scripts can't import files with .cjs extension properly (used in https://www.npmjs.com/package/bs58)
• enable tree-shaking (closes Consider providing a build using es6 imports/exports #194)

[dincho]

➜  aepp-calldata-js git:(esm) make browser-tests
mkdir -p build/js
npm run browser-test-bundle

> @aeternity/[email protected] browser-test-bundle
> browserify tests/[A-Z]*.js tests/**/*.js > build/js/tests.js

Error: Parsing file /Users/dincho/projects/aeternity/aepp-calldata-js/tests/AciContractCallEncoder.js: 'import' and 'export' may appear only with 'sourceType: module' (1:0)
    at Deps.parseDeps (/Users/dincho/projects/aeternity/aepp-calldata-js/node_modules/module-deps/index.js:519:15)
    at getDeps (/Users/dincho/projects/aeternity/aepp-calldata-js/node_modules/module-deps/index.js:447:44)
    at /Users/dincho/projects/aeternity/aepp-calldata-js/node_modules/module-deps/index.js:430:38
    at ConcatStream.<anonymous> (/Users/dincho/projects/aeternity/aepp-calldata-js/node_modules/concat-stream/index.js:37:43)
    at ConcatStream.emit (node:events:531:35)
    at finishMaybe (/Users/dincho/projects/aeternity/aepp-calldata-js/node_modules/readable-stream/lib/_stream_writable.js:630:14)
    at endWritable (/Users/dincho/projects/aeternity/aepp-calldata-js/node_modules/readable-stream/lib/_stream_writable.js:638:3)
    at Writable.end (/Users/dincho/projects/aeternity/aepp-calldata-js/node_modules/readable-stream/lib/_stream_writable.js:594:22)
    at DuplexWrapper.onend (/Users/dincho/projects/aeternity/aepp-calldata-js/node_modules/readable-stream/lib/_stream_readable.js:577:10)
    at Object.onceWrapper (node:events:633:28)
make: *** [build/js/tests.js] Error 1