New traversal algorithms, fractals, performance benchmarks

This release contains many new features:

• stack based traversal methods have been moved to shared workgroup memory - this alone is a massive performance boost (~10x)
• threaded BLAS (stackless traversal that replaces individual instances in the acceleration structure)
• stratified wavelengths for spectral rendering
• LBVH binary AABB construction
• bug fixes

The README has also been extensively updated and there are new demo scenes.