CONC-274: connection string support

A connection string contains key/value pairs, separated by a semicolon
as used in ODBC. Supported keys are all configuration options which can
be used in MariaDB configuration files. For a complete list check
https://github.com/mariadb-corporation/mariadb-connector-c/wiki/config_files#configuration-options.
The connection string must contain at least one semicolon, otherwise
it wil be interpreted as hostname. Unknown or invalid keys will be ignored.

To connect via connection string, the following methods might be used:

- by specifing connection option in configuration file:

  connection=host=localhost;ssl_enforce=1;

-  by using mariadb_connect() macro

   mariadb_connect(mysql, "host=localhost;ssl_enforce=1")

-  by passing connection string in host parameter to mysql_real_connect

   mysql_real_connect(mysql, "host=localhost;ssl_enforce=1", NULL, NULL, NULL, 0, NULL, 0)

include/mysql.h

@@ -882,6 +882,7 @@ struct st_mariadb_methods {
 #define mysql_reload(mysql) mysql_refresh((mysql),REFRESH_GRANT)
 #define mysql_library_init mysql_server_init
 #define mysql_library_end mysql_server_end
+#define mariadb_connect(hdl, conn_str) mysql_real_connect((hdl),(conn_str), NULL, NULL, NULL, 0, NULL, 0)
 
 /* new api functions */