Issue with transaction handling

I faced with the problem that when transaction is failed the connection becomes absolutely useless and further requests lead to exceptions.
 
After looking at the documentation of [postgrsql-async@mauricio](https://github.com/mauricio/postgresql-async) I realized that scalikejdbc-async handles transaction in its own way, while driver already provides such functionality.
Also @mauricio recommends:
> You should not reuse a database connection that has rolled back a transaction, just close it and create a new connection to continue using it.

So I suggest:
- use transaction's handling via driver
- remove code related to the old version of driver

Well, at least these changes work for me and my project