Function interp_title 

fn interp_title(
    _args: &[RValue],
    named: &[(String, RValue)],
    context: &BuiltinContext<'_>,
) -> Result<RValue, RError>

Set or update plot titles.

@param main main title @param sub subtitle (ignored for now) @param xlab x-axis label @param ylab y-axis label @return NULL (invisibly)