[WIP] Implement extensions API

# Work on description is in progress

Add new configuration prop `--extension `

Path can be absolute or relative to node_modules.

Extension is a module with default export.
Default export can implement one or more methods:

```ts
registerOptions(yargs): Promise | void {}

registerTransformer(cliConfig): Promise | void {}

registerIncluder(cliConfig): Promise | void {}
```