PostgreSQL: add connection getter

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: add async processing

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: add fields to query structure

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: alter connection structure

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: add read/write handler

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: remove unnecessary spaces

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: update Makefile.in

Signed-off-by: swpd <swpdtz@gmail.com>
PostgreSQL: fix bugs

Signed-off-by: swpd <swpdtz@gmail.com>