Allow to directly add REST calls to layouts

[Kaliumhexacyanoferrat]

As a developer, I would like to add REST calls directly to layouts, so that my code is easier to read and maintain.

Example

var app = Layout.Create()
                .OnGet("/info", () => "This is info");

Acceptance criteria

• The functionality is implemented on framework level
  • There is a project template for the new framework
  • The framework is mentioned in the docs, in the project site
  • The samples in the concepts section have been adjusted
• The functionality is implemented internally using the Inline builder
• The functionality is implemented in a new module with the name of the new framework
• The feature is documented on the GenHTTP website
• The feature is covered by acceptance tests