provide a bunch of builtins and revamp how they're called
* `cellnum`: The number (integer) of the current cell. Starts at 1
* `cellref`: A reference to the current cell
* `rowabove`: A reference to the row above
* `rowbelow`: A reference to the row below
* `rownum`: The number (integer) of the current row. Starts at 1
* `rowref`: A reference to the current row
* `cellabove`: A reference to a cell above the current row
* `celladjacent`: A reference to a cell in the current row
* `cellbelow`: A reference to a cell below the current row
