Feature add include only

This allows you to use another condition that will check if an array datatype `contains_only` a subset of a given array.

Here is a ruby example to illustrate this:

```ruby
>> [1, 2, 3] - [2, 3]
=> [1]
>> [2, 3] - [2, 3]
=> []
>> [2, 3] - [2, 3, 4]
=> []
```

***NOTE*** As PostgreSQL tricks were getting more and more important, I've decided to completely switch from SQLite to PostgreSQL.