Provide method for deep equivalence with type saftey.

Currently you can do `is` but that will ensure two objects are equal. It would be nice to have a way to ensure all values are equal and the correct type.

```
expect({a:5}).to.eql({a:"5"}); // Passes.
```

It would be nice to have this as I have objects with many properties and it is a pain to manually `.is()` check each property.

So it would be nice to have something that strictly compares types if "scalar" values (including strings). And recursively compares objects and Arrays.

Start by reading the existing `is` and `eql` assertion behavior, using the object example in the issue to reproduce the current result. The change is done when a deep comparison rejects scalar values with different types while recursively comparing nested objects and arrays.

Written by the indexing model from the issue text.