0.2.0 Release: Workshop, Stat Bars, Turrets

My dumb prototype is now a little more like a proper game! Just a little, though. I've even thought about giving it a name. But I think that can wait until it has more depth than "shoot balloons/turrets or race the developer".

The major additions are a workshop, health/fuel/energy systems, and hostile turrets.

Full v0.2.0 changelog:

- Added dynamic HUD markers for objects of interest.
- Corrected player vehicle's scale (was undersized).
- Added air base to main world.
- Added workshop, accessible by flying into an icon above the air base.
- Camera distance can be adjusted with the mouse wheel.
- Added turrets to main world.
- Smoothed sky gradients.
- Brightened slider button.
- Added health/fuel/energy bars and mechanics.
- Added combat music.
- Workshop: Added a button to repair vehicle (costs 10 points).
- Jet model: Tweaked shape, added engine intakes, optimized collision.
- Improved projectile impact effect.
- Added crosshair marker that flashes when the player hits a target.
- Workshop: Added refuel button.
- Added high score counter on death.
- Renamed "Target Practice" to "Free Flight".