Investigate "method" routing

[CathalMullan]

Need to be able to support any number of methods, or all.

Custom methods too.
Maybe we can create a quick path for standard methods, then custom methods can use a seperate path?

So our search should be able to handle:

• no method filter
• single method
• methods
• all methods

For method routing specifically, we need to support the "Method Not Supported" response too.

We'll want to abstract over data storage - e.g. data can be stored inline as T/Arc at any layer.

Do we want to support route without a path?
Yes - why not.

Annoying that http::Request isn't no_std compatible.
UPDATE: Well now it is: https://github.com/DuskSystems/http

Conflict handling may be tricky.

Should update the GitLab examples to use method.

let mut router = Router::new();
router.path.constraint::<C>();

let route = Routable::builder()
    // or: .methods(vec![..])
    .method(Method::GET) 
    .method(Method::HEAD)
    .route("/users/{id}")
    .build();

router.insert(route, handle_users_by_id)?;

Before we tackle this - we should:

• setup a request builder
• move existing router to be named path router
• create a top-level meta router
• change match to support multiple matching routing targets
• setup a route builder
• add a better abstraction over data storage (i.e. data should be top-level, not per router)