Update 0.38

This update brings some optimizations and a new world type (mountains). The game now uses vertex shader textures, so I had to drop support for some old Radeon cards that don't support this feature.

Change log:

• New world type: mountains.
  
• Using vertex shader textures for height map and water foam flow (moving some calculations to GPU).
  
• Smoother nearby land (clamped bicubic interpolation).
  
• Culling out-of-view land, water and lava.
  
• Fixed guard tower shooting at mana gatherers.
  
• Various minor improvements.