Add Marko support

[Heziode]

Hi, I work one electron project using Marko.

When I compile (with webpack), it failed because x-button,etc are not defined templates.

Solution I found ?

Just create a marko.json at the root of project and describe all tags with attributes. Exemple :

{
  "tags": {
    "x-input": {
      "attributes": {
        "type": "string"
      }
    },
    "x-icon": {
      "attributes": {
        "name": "string",
        "iconset": "string"
      }
    },
    "x-label": {
      "attributes": {
        "data-vivaldi-spatnav-clickable": "number"
      }
    },
    "x-button": {
      "attributes": {
        "data-vivaldi-spatnav-clickable": "number"
      }
    }
  }
}

Possible improvement, add an marko.json at the root of project who discribe all tags with attributes ?

[jarek-foksa]

I would prefer to not include any framework-specific code in this repo. Please create a separate xel-marko project with necessary adjustments.