proposed fix for #147

[hoosierEE]

This change does 2 things:

1. adds a url_prefix option in the toml file so you can specify a prefix for the generated .js file to be used index.html
2. makes the default prefix "" instead of "/" so that your webserver can be in a different directory. This addresses issue Add configuration option to use relative links #147

[hoosierEE]

Add this to your gleam.toml file to restore the original behavior:

[tools.lustre.html]
url_prefix = "/"

[hayleigh-dot-dev]

Hey, thanks for exploring this! There's a bit more to consider in a way that makes this tricky because we also handle static assets.

Assets get placed in the top-level assets/ directory and then are served during development, so a file like assets/img/wibble.png would be available at /img/wibble.png.

If we have a configurable base url for builds, how will that affect the source code that needs to reference these assets?