No, "Craft Wars" is not the latest hit reality show featuring dueling teams of art majors: it's the newest Heroes of the Storm event.
It means exactly what it says, in that it combines Starcraft and Warcraft into one game, something Heroes does quite well already. Don't get too excited though, as Craft Wars is basically a cosmetic event. You'll need to buy the skins featured in it with shards (in-game currency) or gems (premium), but there's a few great ones on offer here, as well as some badass art.
Death Knight Mei is a standout, as well as SCV Pilot Gazlowe and King of Blades Arthas (what a crossover). The event comes hand-in-hand with complete reworks for D.va and Gazlowe, which have had opposite reactions from the playerbase thus far; with folks enjoying a (potentially overtuned) D.va while wanting some of Gazlowe's changes to be rolled back.
Another huge change: everyone gets a self-cleansing item at the start of the game with a huge cooldown, and Brawl has been eliminated in favor of making it a full-time ARAM mode. So far this update has been a wild ride, and has injected a fair bit of life into the game following a staggered lower-impact balance patch cadence.