Drop-in replacement for wkhtmltoimg #3

It will be nice if this library can be used for drop-in replacement for wkhtmltoimg. It will be very useful for cases when you need to generate some previews for your entries (e.g. for news site, blog, etc). wkhtmltoimg have some issues that makes this so bad. For example I can't use custom fonts from external site like Google Font because library renders content before fetching all required resources.