Add handler for static websites

[Kaliumhexacyanoferrat]

A a developer of a static website, I would like to use the GenHTTP framework to simply host my static content in a few lines of code.

Example

var website = StaticWebsite.From(ResourceTree.FromDirectory("./hugo/public/"));

Host.Create()
    .Handler(website)
    .Run();

Acceptance criteria

• The functionality is implemented in a new module
• The handler provides an index page for every folder where such an index file exists (e.g. "index.html"). Otherwise a HTTP 404 is returned
• The handler serves a sitemap, if none does exist as a file