Don't require closures

[mateusjatenee]

I don't think we need to explicitly require closures when adding columns — if one isn't passed, we can infer that it refers to an attribute of the model.

The PR also requires a small refactor and naming changes. Let me know if you want to remove those!

[mateusjatenee]

Another suggestion — right now it always uses the id property to sort the collection. Now, there are two other possibilities: 1) the model's primary key isn't ID and 2) the data doesn't have an ID at all.

Supporting 2 would give this package the ability to generate datatables to anything at all — not only Eloquent models.
Now, this requires further changes and I didn't want to add in this PR. Let me know if you want some help!

[luanfreitasdev]

I found the functionality very valid and useful !.

This made the code much cleaner and more usable.

You can send the PR that together we will make a quality datatable

Thanks @mateusjatenee