beta-2.9: Level 4.

New Features

• Added Level 4, where 2 triangles guard the square and 3 others patrol.
• Added a health power-up (the blue circle) in Level 4, that fully replenishes the player's health when found. It is - like the square - not visible unless within the light's range.
• The Health text's colour changes to blue when it increases, and to red when it decreases.