FluidX3D v2.15 (framerate boost)

Thank you for using FluidX3D! Update v2.15 boosts framerate in interactive graphics by 20-70%:

• eliminated one frame memory copy and one clear frame operation in rendering chain
• enabled g++ compiler optimizations for faster startup and higher rendering framerate

Bug fixes:

• fixed bug in multithreaded sanity checks
• fixed wrong unit conversion for thermal expansion coefficient
• fixed density to pressure conversion in LBM units
• fixed bug that raytracing kernel could lock up simulation
• fixed minor visual artifacts with raytracing
• fixed that console sometimes was not cleared before INTERACTIVE_GRAPHICS_ASCII rendering started

Have fun with the software!
-- Moritz