Batch operations on multiple tables encapsulation

[GingerMoon]

Use cases:

1. Single entity: Employ{id, first name, second name, nick name, age}
   I want to search by nick name, so I will have two tables for this single entity:
   employ and employ_by_nickname. (I don't want to use materialized view)
   I need encapsulations including the CRUD, find_by_id, find_by_nickname, update "nick name".
   (In order to udpate "nick name", I need to delete the existing one first because nick name is the partition key of employ_by_nickname.)

2. Multiple entities (one table for every entity). Create, update, delete needs to be in the same batch.

I'd like to contribute the encapsulated code. Will you be interested?

[mmatczuk]

YES, Batch support is very poor at the moment.

Relates to #110

[GingerMoon]

Thanks @mmatczuk for the interest. I made a PR as a draft version for the purpose of POC.
The code has't been carefully polished yet.
Please just have a quick look and let me know if this is what we want.
Then I will spend some time on polishing the PR.