Add option to specify font size

[Satyam]

The font sizes on the PDF are humongous. If it is not possible to specify individual font sizes, with options like --body, --h1, --h2, which would be too tedious, perhaps an option just to set a general size or scale, like --font-size small.

Also, with requests for extra options multiplying, as they will sure be, it might be a good idea to plan for a docusauros-pdf.config.js file or some such.

Thanks

[kohheepeace]

@Satyam sorry for the super late reply 🙇

1. For font size in PDF, it may be solved by using @media print.

@media print {
  body { font-size: 10pt; }
}

2. config file like docusauros-pdf.config.js is really nice feature, PR is welcome 👍