Add function default_options() to beautifier.js

[tkrotoff]

You can retrieve Beautifier default options using Python: opts = jsbeautifier.default_options(), not with JavaScript.

This would be useful for "complex" default options, example with beautifier.js source code for unformatted:

// beautifier.js simplified source code for unformatted
// https://github.com/beautify-web/js-beautify/blob/v1.7.5/js/src/html/beautifier.js#L93
defaultOptions.unformatted = [
  'a', 'abbr', 'area', 'audio', 'b', 'bdi', 'bdo', 'br', 'button', 'canvas', 'cite'
  // ...
];

If I want to remove (or add) some tags from the unformatted option I would like to write something like:

import { html_beautify, defaultOptions } from 'js-beautify';

const excludeButton = defaultOptions.unformatted.filter(tag => tag !== 'button');
const niceHtml = html_beautify(uglyHtml, { unformatted: excludeButton });

[bitwiseman]

@tkrotoff Sounds great! Go for it.

[bitwiseman]

Fixed by #1568.