v0.3.4

Refactored and added some methods.

• order_by() now you can use multiple fields for sorting (use a list like ['field1', 'field2 desc'])
• group_by() now you can use multiple fields for grouping (use a list like ['field1', 'field2'])
• where() and having() now you can omit the operator = or IN, usage where([['id', 3]]) and where([['id', [10, 11, 12]]])
• method pluck(key_index, column_index) returns a list of tuples of needed columns