Add parameters that correspond to MYSQL_READ_DEFAULT_FILE and MYSQL_READ_DEFAULT_GROUP options from MariaDB Connector/C

MariaDB Connector/C allows an application to read a MariaDB configuration file, and it also allows the application to specify the option group within the configuration file. The MYSQL_READ_DEFAULT_FILE and MYSQL_READ_DEFAULT_GROUP options are used for this:

MYSQL_READ_DEFAULT_FILE:

MYSQL_READ_DEFAULT_FILE: Read options from named option or my.cnf. To read from the my.cnf file a NULL pointer has to be passed instead of a file name.

mysql_optionsv(mysql, MYSQL_READ_DEFAULT_FILE, (void *)"./my_conf.cnf");

MariaDB Connector/C will not read the configuration by default. If MYSQL_READ_DEFAULT_FILE is specified the following sections will be always processed:

[client]
[client-server]
[client-mariadb]

MYSQL_READ_DEFAULT_GROUP:

MYSQL_READ_DEFAULT_GROUP: Read options from the named group from my.cnf or the file specified with MYSQL_READ_DEFAULT_FILE.

mysql_optionsv(mysql, MYSQL_READ_DEFAULT_GROUP, (void *)"my_section");

https://mariadb.com/kb/en/library/mysql_optionsv/#options

It might be useful if MariaDB Connector/ODBC allowed users to configure an ODBC data source to read options from a configuration file.