2d not supported in virtuals

[cbchouinard]

We should add arithmetic operation support for 2d in virtuals. For example the following doesn't work:

sq2 {

  height: == "quater"[height] / 4;
  width: == "quater"[width] / 4;
  **position: == "quater"[top-right] / 2;**
}

When adding an arithmetic operation after the 2d property it generated an AST using the name of the 2d property.

[d4tocchini]

2D props work with virtuals, but just found out they don't work nested in expressions...

[cbchouinard]

I'll try to extract the 2d expressions from the AST instead of at the parsing stage.