Mutations: better transaction / atomicity guarantees

[Totktonada]

• perform atomic mutations -- aupdate and so on? other rules for shown
  result and other constraints (say, we can check all changes will going to the one storage);
• use q_* operations to give some guarantees?
• or we can just provide a request metainfo (static one, available after compile) to give user know whether it is transactional?

By the way, we can provide better guarantees with space_accessor too, using box.begin() / box.commit().

Follow up of #142.

[Totktonada]

We should at least call begin / commit functions of an accessor to allow a user to implement its own transactions mechanism.

[Totktonada]

I'm going to archive the repository. I'll proceed as follows:

• Mark all open pull requests with the archived label and close.
• Mark all open issues with archived and wontfix labels and close.
• Archive the repository.

Consider the following projects:

• https://github.com/tarantool/graphql
• https://github.com/tarantool/graphqlapi
• https://github.com/tarantool/graphqlide