Veinminer++

Added

• Rebindable vein-mine activation key — a new Vein-mine (hold) keybind (unbound by default; set it in Controls). Hold it while breaking a block to vein-mine. A new Sneak activates option (on by default) keeps the classic hold-Sneak trigger, or turn it off to require your own key so you can crouch without vein-mining.
• Toggle vein-mining keybind — a new Toggle vein-mining keybind (unbound by default) flips vein-mining on and off on the fly, with a chat message only you can see. Resets to on each time the game launches.