Enum support

[hauke96]

Add enum support. To create a good structure, rename the "schemes" root element into "classes" and add "enums" next to it. This scheme structure should do the trick:

{
  "classes": [...],
  "enums":
  [
    {
      "name": "TestEnum",
      "fields":
      [
        "ACTIVE",
        "DEACTIVE",
        "UNDEFINED"
      ]
    }
  ]
}