Add Ambient Occlusion Support.

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Different Ambient Occlusion Techniques:

• Horizon-Based Ambient Occlusion (HBAO) Whitepaper.
• Real-Time Depth Buffer Based Ambient Occlusion
• Dynamic Ambient Occlusion and Indirect Lighting
• Screen Space Ambient Occlusion (SSAO)

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Adding Ambient Occlusion could also solve the problem described in issue #27 .