fix: Improve TypeScript support

[micksatana]

Hi @santigimeno,

Thanks for this great lib! I'm using it to develop on one of my project. I've come across some issue with TypeScript when I want to organize handler functions without nesting them too much. Like the following..

import PCSCLite, { CardReader } from 'pcsclite';

const pcsc = PCSCLite();

const onReaderError = (e: Error) => {
    console.log(e.message);
};

const onReaderDetected = (reader: CardReader) => {
    // Listen to all other reader events here; for example,
    reader.on('error', onReaderError);
};

pcsc.on('reader', onReaderDetected);

The problem with the current code will be the CardReader as it's not exported and the types is not specified in package.json. This causes the onReaderDetected above having type issue.

I've made some adjustment to make this work. Please consider my PR, if it's ok to merge.