Function mg::blocking_question

pub fn blocking_question<COMM, SETT>(
    mg: &EventStream<<Mg<COMM, SETT> as Update>::Msg>, 
    msg: String, 
    choices: &[char]
) -> Option<String> where
    COMM: Clone + EnumFromStr + EnumMetaData + SpecialCommand + 'static,
    SETT: Default + EnumMetaData + Settings + SettingCompletion + 'static, 

Ask a multiple-choice question to the user and block until the user provides it (or cancel).