Feature Request: Downloads

I would like to use this extension for a simple http fileserver client. However, downloads are not supported. Would it be possible to add this functionality?

To recreate my use case:
- in terminal run `python3 -m http.server` (runs a local http fileserver from whatever folder location you are in)
- in browser-preview navigate to `http://localhost:8000/`
- click on file to download (doesn't work)

Reproduce the issue by running `python3 -m http.server`, opening `http://localhost:8000/` in browser-preview, and clicking a file. Trace how the extension handles navigation and determine the download behavior needed; done means files served by the local HTTP server can be downloaded from the preview.

Written by the indexing model from the issue text.