Add bind.radio

[Tarmil]

For radio button groups.

module bind =
    val radio : group:string -> thisButtonValue:string -> onChecked:(unit -> unit) -> Attr

// Example use:
let myRadioList model dispatch =
    forEach {1..10} <| fun ix ->
        input [
            bind.radio "mygroup" (string ix) (fun () -> dispatch (SetMyGroup ix))
        ]

// Equivalent to:
let myRadioList model dispatch =
    forEach {1..10} <| fun ix ->
        input [
            attr.``type`` "radio"
            attr.name "mygroup"
            attr.value (string ix)
            on.change (fun args ->
                if (args.Value :?> string) = string ix then
                    dispatch (SetMyGroup ix))
        ]

[Tarmil]

It turns out that the following is sufficient:

let myRadioList model dispatch =
    forEach {1..10} <| fun ix ->
        input [
            attr.``type`` "radio"
            attr.name "mygroup"
            bind.change (string ix) (fun _ -> dispatch (SetMyGroup ix))
        ]

So I think we don't actually need a separate bind.radio function; users can write the above to create a radio button. Similarly to how bind.changeInt and family don't implicitly add attr.``type`` "number".

We should document this though.

[Tarmil]

Documentation added.

[Morranr]

The HTML templates documentation page (Templating.md) still shows the note about radio buttons not being supported, which I assume should be updated similar to the Writing HTML page (HTML.md) in the above referenced commit.

[Tarmil]

Good catch! I believe we should also make it so that bind="${Name}" defaults to onchange for type="radio".