Create resource from HTTP

[Kaliumhexacyanoferrat]

As the developer of a web application, I would like to create resources from HTTP, so that I can use them where needed.

Example

var resource = Resource.FromWeb(/* url, credentials */);

Host.Create()
    .Handler(Download.From(resource))
    .Run();

Acceptance criteria

• The functionality is implemented in the IO module
• The functionality uses an efficient checksum algorithm (HEAD request, eTag, ...)
• The functionality uses a well tested, mature, maintained .NET class to issue requests (e.g. HttpClient)
• The connection is created and disposed on the fly where needed (must be thread-safe)
• The handler does not expose internal, client-specific types (e.g. network credentials)
• Credentials can be passed (e.g. via a lambda setting the Authorization header)
• There are acceptance tests for the new functionality (using the webserver provided by the runner itself)