Quarto should output websites with "pretty" URLs

When using quarto to build websites, some static site generators, for instance mkdocs, create sites with "pretty" URLs by default. It would be great if Quarto also did this.

For instance, in a project containing the file science.md, quarto render will generate that as science.html, resulting in a URL like, https://example.com/science.html. In contrast, mkdocs build would generate it as science/index.html, meaning that, when published, it could be accessed at https://example.com/science/.

The current workaround would be to create the original file at science/index.md, in which case, both quarto and mkdocs would generate the same HTML in the same places.

This is important for sites that might be considering migrating to quarto that are not currently structured along the lines of the workaround.

Start with the website rendering behavior exercised by quarto render and compare the science.md and science/index.md examples. Trace where output paths are chosen, then verify that science.md produces science/index.html and a published /science/ URL without breaking the existing workaround.