Parametrized templates

[Jakub21]

In SHP v1 it was possible to use a (very rough) workaround to create parametrized templates. Because v2 has no namespaces, it no longer is possible.

Implement a proper system for parametrized templates.

Proposed / example usage:

// define the template
@template[#ExampleTemplate] {
    $div[.Example] {
        $h3 { @slot[#Name] }
        @slot[#Content]
    }
}

// insert twice with different parameters
$div[#Listing] {
    @insert[template = ExampleTemplate] {
        @param[#Name] {Hello}
        @param[#Content] {
            $img[src = "/img/hello.png"]
            Hello world\!
        }
    }
    @insert[template = ExampleTemplate] {
        @param[#Name] {Goodbye}
        @param[#Content] {
            $img[src = "/img/bye.png"]
            The end\!
        }
    }
}

Because SHP functions are executed after the tokens are already parsed into nodes, I doubt it would be possible to parametrize something that is not itself a node (for example, tag parameters).