Maintain primary key type specificity

[danielwestendorf]

Partially fixes #172.

Previously schema would be dumped as such:

create_table "my_table", id: :integer, limit: 2, unsigned: true do |t|
...
end

limit and unsigned would be ignored, resulting in an incorrect representation of the schema.

After it will specify the correct Clickhouse-native type:

create_table "my_table", id: :uint8 do |t|
...
end

It does not address non-id named primary keys.