## Details

- This PR basically reverts PR #32 because this is hell. More about this in **Why???** section below.
- Only generate CommonJS code in `lib/` instead of both ESM and CommonJS code.
- Remove Babel stuff and rely on `tsc` to generate CommonJS code and TypeScript declaration files in `lib/`.

## Why???

- Because this is hell. Totally hell.
- Before this PR, rtp.js can not be used in TypeScript projects that use Webpack to generate a bundled JS file. Why? Because Webpack assumes that everything is CommonJS but then it miserably fails to locate/resolve '.cjs' files.
- If we have '.ts' files in `src/` folder, then `tsc` will generate 'js' files rather than '.mjs' files, and that means problems with loaders/bundlers that assume that '.js' files contain CommonJS and then they fail to process them because those '.js'  files contain 'import/export' rather than 'require/module.exports'.
- And if we have '.mts' files in `src` then `tsc` will generate `.mjs` with ESM code but it's literally impossible to have another `tsconfig-cjs.json` file to make `tsc` generate CommonJS code.
- So then we moved to Babel to generate ESM and CJS code (see PR #32), and we have to include tricks to replace the extension in the `import` and `require()` calls in the generated ESM and CJS code in `lib/`, which is terrible. But then Babel also generates `.js.map` files that reference a `.mts` file in `lib/` folder which obviously doesn't exist.
- And another problem is that Babel only generates JavaScript code so we still need to use `tsc` to generate TypeScript declaration files and, since we have '.mts' files in `src/`, those declaration files have `d.mts` extension. But they many text editors and TypeScript consumers asusme that declaraion files must be '.d.ts' only. And if we rename their extension then we have also to munge generated `.mjs` (ESM) and `.cjs` files in `lib/` because those files contain special commented mapping lines that reference the declaration file (with '.d.mts').
- And then it also happens that in CommonJS importing a file without extendion is ok, but in ESM you must write `import foo from './foo.ts'` rather than `from './foo'`. So here another needed rewrite in generated `lib/` code.
- etc etc etc, and **trust me**, more etc etc etc. I've tried EVERYTHING, much more than what I've told here.

## Conclusion

- It's impossible to generate ESM and CJS file in a proper way because it entirely affects the way the TypeScript code must be written, and it includes whether to use `.ts` or `.mts` extension in source files, whether to import internal files with or without extension, and `tsconfig.json` doesn't expose options enough to cover all cases we need when generating ESM or CJS code. I've checked them all, and the same with Babel.
- My conclusion is that, if you want to publish a library in ESM format, you only generate ESM code ('.mjs' files) from TypeScript '.mts' files. But you cannot generate **also** CJS files. And the other way around.