This update brings a quick button for using potions! It will automatically use the optimal potion based on your remaining health. To activate, when using keyboard and mouse, press 1 (as indicated on the HUD), and with a controller, press left on the Dpad.
Note that with this update, the Dpad will no longer work for movement of your character, but you can still use it to navigate the UI.
A future update will allow this button to be modified, as with all other keys.