Multidimensional loops

Basic idea: When we can have multidimensional arrays (like `fields[row][column]`), we should also be able to easily loop through them:
```coffee
    for field, column, row in fields
      console.log "(#{row}|#{column}) has value #{field}"
```

The old way for this is (or at least that's how I always did it):
```coffee
    for row, rowid in fields
      for field, columnid in row
        console.log "(#{rowid}|#{columnid}) has value #{field}"
```
*(edit: corrected that example, thanks michaelficarra)*

Another example (from the testcase):
```coffee
    cells = [[0,1],[3,4]]
    cellsIncreased = (cell+1 for cell, y, x in cells)
```
`cellsIncreased` is `[[1,2],[4,5]]` now

The syntax is:
```coffee
    for <name>, <lastindex>, ..., <secondindex>, <firstindex> in <array>
```