Use sql kata for handle multiple database

[GiuseppePatane]

Hi, first of all I wanted to thank you for this project. I tried using it because I was interested in better performances. Since the db I tested is on Postgres I thought we could make the library more flexible by adding [SqlKata].(https://sqlkata.com/) This library is in short word a query builder for actually:

• Sql Server
• SQLite
• PostgreSql
• MySql
• Oracle
• Firebird

The other change I had to make concerns the connection management. I did a load test with JMeter (6000 in 30 second x 10 cicle), and i found a problem on having the connection creation inside the IdentityTable ctor.

Let me know what you think and if it looks ok to you.