Enable execution of multiple sql statements in execute_sql_string independent of db api #252

The database-library currently provides the handling of multiple sql statements when working with files by splitting the file content into single statements using an external sql parser or an own mechanism.

Executing multiple statements in a string sql query currently relies on the database api being able to handle the multiple statements in the string.

As not all database api's provide this functionality, the ability to work with multiple strings should be provided by the database library using sql parsers.