Implemented to assign C data type to mrb_get_config_value args

mrb_get_config_value(mrb, key, format, ...)
mrb_get_sub_config_value(mrb, tag, key, format, ...)

format specifiers (like mrb_get_args):

 o: Object [mrb_value]
 S: String [mrb_value]          //Not Implemented
 A: Array [mrb_value]           //Not Implemented
 H: Hash [mrb_value]            //Not Implemented
 s: String [char*,int]          //Not Implemented
 z: String [char*]
 a: Array [mrb_value*,mrb_int]  //Not Implemented
 f: Float [mrb_float]           //Not Implemented
 i: Integer [mrb_int]