Add support of MSSQL ODBC

As of first congrats for this package - I'm using it quite often & it's a great help.

I'd like to ask a feature request - add support for MSSQL DB.
The main official mode of connection recommended by MS is ODBC/PDO.
https://docs.microsoft.com/en-us/sql/connect/odbc/linux-mac/installing-the-microsoft-odbc-driver-for-sql-server?view=sql-server-2017#microsoft-odbc-driver-17-for-sql-server

As far as I've tested it could be pretty the same as 'sqlsrv' driver but the following differences:

• GenericDB: getOptions\PDO::SQLSRV_ATTR_DIRECT_QUERY &
  PDO::SQLSRV_ATTR_FETCHES_NUMERIC_TYPE are not valid options in case of MSSQL ODBC PDO - so please remove them on the new driver case.

• GenericReflection: getTableColumnsSQL and getTablePrimaryKeysSQL - please remove unnecessary "and '' <> ? " query parameter from the end as it fails during execution.

• GenericDB: getDSN would require an additional driver case parameter where direct DB DSN could be specified eg: could come as Config parameter.

Sorry not sending as direct pull request - but I'm new contrib on github, whoever would be happy to help with testing.