Short array notation

As seen on da4c0d70949c61b138bf58f86cb8319ee430ff2c, it seems to be the time to switch to the short array notation.

I know this is a huge PR to review @taylorotwell and that many people will have to rebase their branches against master.

FYI, to "ease" a bit the review, I've been making 4 spearate commits