Add yn_yes and yn_no

[ChillerDragon]

yn_yes is a function that takes a string and then acts as a prompt. The implementation could look like this:

functuion yn_yes() {
        read -p "$1 [Y/n]" -n 1 -r
        echo 
        if [[ $REPLY =~ ^[Yy]$ ]]; then return 1; fi
}

A use case might be:

if yn_yes "do you really want to do xyz?"
then
       proceed
fi
exit

And yn_no is the default no case.

[ChillerDragon]

Also yn_abort could come in handy. It can be invoked after a critical warning if the user wants to continue or quit the script.