Block state support

[null2264]

Previously reported on GH-9, as block state no longer used for variant I thought it probably fine not implement it.

Format:

{
  "id": "minecraft:door[open=false,...]"  // One-liner, separated by comma
  // or
  "states": {
    "open": false,
    ...
  }
}
// for modifiers
"cobblegen:modifier[powered=true,...]": [  // One-liner, separated by comma
  {
    ...,
    // or
    "modifierStates": {
      "powered": true
    },
    ...
  }
]