Allow for each function's bin path to be seperately defined

[Fdawgs]

Prerequisites

• [X] I have written a descriptive title

• [X] I have searched existing feature requests to ensure it has not already been proposed

• [X] I agree to follow the Code of Conduct that this project adheres to

Description

At present, all functions use the popplerPath property for their bin path.

This should be broken down to an individual level so that it can be modified if needs be:

const { Poppler } = require('node-poppler');

const poppler = new Poppler('/usr/bin');

poppler.pdfToTextPath = '/totallydifferentpath/bin';
poppler.pdfToHtmlPath = '/anotherpath';

await poppler.pdfToText(new Buffer('bleh'));