Add git updating to execution

[zaanposni]

As there has been some mistakes on the master branch, I would suggest to add something like

git fetch 
git pull origin master

To the execution when running cloudflare-ddns --update-now.
This update process can be made optional by asking the user during cloudflare-ddns --configure if he would like to receive updates.

What are your thoughts on that @LINKIWI ?

[zaanposni]

Also do you mind to use some kind of IRC to communicate?
I propose Gitter or Discord.