Various documentation enhancements.

include/PolyVox/DefaultIsQuadNeeded.h

@@ -31,6 +31,15 @@
 
 namespace PolyVox
 {
+	/// Default implementation of a function object for deciding when
+	/// the cubic surface extractor should insert a face between two voxels.
+	///
+	/// The criteria used here are that the voxel in front of the potential
+	/// quad should have a value of zero (which would typically indicate empty 
+	/// space) while the voxel behind the potential quad would have a value
+	/// geater than zero (typically indicating it is solid). Note that for
+	/// different behaviour users can create their own implementation and pass
+	/// it to extractCubicMesh().
 	template<typename VoxelType>
 	class DefaultIsQuadNeeded
 	{