GPL'ed it. Hopefully no one will have a problem re-using this code :)
Considering Notch licensed his using BSD; it would have been a nice gesture to keep the same unrestrictive license.
But that's your choice.
Isn't all the source code published in public github repos GPL by default?
No. You must explicitly state what the license is. Otherwise, in most countries no one but the author and authorized parties have the right to redistribute it or use it.
Not even close. By default there is no license at all.