RFC for Chef 12 Attr changes

`rm_default!` isn't a thing, but assuming that's just a typo, no they are not the same... though depending on the values stored they could act the same. However, these two are the same:

```
node.force_default!['foo'] = { "johnny" => 5 }
```

and

```
node.rm_default('foo')
node.force_default['foo'] = { "johnny" => 5 }
```