Can we add ESM support?

[monim67]

Right now in ESM we need to puck out the default property

import createSubject from "rx-subject";

console.log(createSubject);
// logs { default: [Function: e] }

[monim67]

We need to use another package if we are using typescript to retain proper types

import createSubjectCjs from "rx-subject";
import { defaultImport } from "default-import";

const createSubject = defaultImport(createSubjectCjs);
console.log(createSubject);
// [Function: e]