Added gpUpdateAD.m file (moved out of gpUpdateKernels.m).
Added gpUpdateAD.m file (moved out of gpUpdateKernels.m).

SheffieldML/forkedGPmat,SheffieldML/GPmat,TianpeiLuke/GPmat,SheffieldML/GPmat,SheffieldML/GPmat,SheffieldML/GPmat,TianpeiLuke/GPmat,TianpeiLuke/GPmat,TianpeiLuke/GPmat,SheffieldML/GPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,TianpeiLuke/GPmat,SheffieldML/forkedGPmat,SheffieldML/GPmat,SheffieldML/forkedGPmat,SheffieldML/forkedGPmat,TianpeiLuke/GPmat