Merge pull request #22 from EmilWestergren/master

Added GPU pyramid generation
Pyramid generation shader optimization.
Merge pull request #23 from fredrikbryntesson/master

Pyramid generation shader optimization.
Removed high precision float for Android pyramid generation shader.
Merge pull request #24 from fredrikbryntesson/master

Removed high precision float for Android pyramid generation shader.
Added Viewport class and adapted other classes to use it