add MYSQL_READ_DEFAULT_FILE and MYSQL_READ_DEFAULT_GROUP options

via "read_default_file" and "read_default_group" connect options

from the man page:

> These options can be used to read a config file like /etc/my.cnf or ~/.my.cnf. By default MySQL's C client library doesn't use any config files unlike the client programs (mysql, mysqladmin, ...) that do, but outside of the C client library. Thus you need to explicitly request reading a config file, as in