Add PDF mapfile compatibility

[JamesErrington]

First part of Auto Street-O project (needs a name)

Looks like PDF.js is the way to do it https://github.com/mozilla/pdf.js/

[JamesErrington]

JS api to convert from PDF https://bytescout.com/products/developer/cloudapi/how-to-convert-pdf-to-image-in-javascript-and-jquery-using-cloud-api-low-level

appears to be the only JS thing around.

Otherwise could try in PHP server side