Feature request: line/column numbers

[AlexanderZeilmann]

Would it be possible to add the line/column numbers of the starting and ending points of the tokens to the AST? Something like

{
  "type": "Identifier",
  "value": "color",
  "position": {
    "start": {
      "line": 2,
      "col": 14
    },
    "end": {
      "line": 2,
      "col": 18
    }
  }
}

Btw, this is one of the best css parsers, I found so far. Keep up the good work :-)