approx and deepApprox to safely compare numbers

Testing equallity of numbers is a tricky business because of possible round of errors in floating point numbers. For example the following test will unexpectedly fail as the result of the left expression is `0.22000000000000003` and not `0.22`.

``` js
test.equal(2.2 / 10, 0.22);
```

It would be great to have functions like `approx` and `deepApprox` to safely compare numbers and objects/arrays containing numbers against each other. The function should compare whether the difference between the two numbers is at least a predefined factor epsilon smaller than the values itself (I guess there will be some edge cases when one of the values is zero, NaN, or Inf).