Request - Please provide typescript support

# About

In order to work with a more modern Javascript environment it would be nice to also provide types that can be installed via yarn or npm: 

- yarn add -D @types/js-son-agent
- npm install --save-dev yarn add -D @types/js-son-agent

Also update the readme to include examples with TS syntax. E.g: 

```
import { Belief, Plan, Agent, Environment } from 'js-son-agent';
```