New learnable ability: Heal

• Hold the left mouse button to slowly restore health, at a rate of 5 HP per second
• Available at the very beginning of the skill tree

• This was way too powerful to be a permanent ability, so it was removed from the skill tree and turned into a rare, single-use item
• This item drops from Metal Core boss in small quantities
• Fixed an issue that was causing the black hole to reward the player with massive amounts of XP for "mining" tiles that are already empty

• Flamethrower's secondary ability is now a talent that has to be learned.
• This is to ease the learning curve and not overwhelm the player with an extra long description of a single ability.

• Key bindings can now be changed for most actions, including the action bar slots, and key binding settings are now properly saved
• Nodes in the talent tree are now much smaller and closer to each other, making the whole thing easier to read. Currently the whole skill tree fits on the screen without needing to scroll.

• Fixed a rare crash related to the frozen orb trying to target enemies that are already dead