Graceful operations

get items with pythonic operations like pandas.

```py
db = Database()
query1: Query = Key('age') < 30
query2: Query = Key('name') == 'Bruce'
db.find(query1 & query2) # -> list of items
```

or

```py
cond1: Condition = Query.Key('age') < 30
cond2: Condition = Query.Key('name') == 'Bruce'
db.find(Logical.And(cond1, cond2)) # -> list of items
```