general tidying in sparse_GP_regression
general tidying in sparse_GP_regression

Have also made a small ampount of headway in
enabling heteroscedatic noise.

dhhjx880713/GPy,avehtari/GPy,beckdaniel/GPy,mikecroucher/GPy,PredictiveScienceLab/GPy,buntyke/GPy,Dapid/GPy,SheffieldML/GPy,TianpeiLuke/GPy,ptonner/GPy,avehtari/GPy,befelix/GPy,buntyke/GPy,avehtari/GPy,SheffieldML/GPy,ptonner/GPy,ysekky/GPy,AlexGrig/GPy,gusmaogabriels/GPy,esiivola/GPYgradients,TianpeiLuke/GPy,befelix/GPy,Dapid/GPy,beckdaniel/GPy,jameshensman/GPy,jameshensman/GPy,buntyke/GPy,PredictiveScienceLab/GPy,maaskola/GPy,AlexGrig/GPy,beckdaniel/GPy,SheffieldML/GPy,esiivola/GPYgradients,ysekky/GPy,fivejjs/GPy,strongh/GPy,mikecroucher/GPy,maaskola/GPy,befelix/GPy,jameshensman/GPy,TianpeiLuke/GPy,Dapid/GPy,mikecroucher/GPy,ptonner/GPy,dhhjx880713/GPy,buntyke/GPy,befelix/GPy,fivejjs/GPy,strongh/GPy,maaskola/GPy,esiivola/GPYgradients,maaskola/GPy,ysekky/GPy,beckdaniel/GPy,PredictiveScienceLab/GPy,gusmaogabriels/GPy,gusmaogabriels/GPy,dhhjx880713/GPy,avehtari/GPy,SheffieldML/GPy,ysekky/GPy,mikecroucher/GPy,AlexGrig/GPy,ptonner/GPy,AlexGrig/GPy,PredictiveScienceLab/GPy,Dapid/GPy,dhhjx880713/GPy,esiivola/GPYgradients,jameshensman/GPy,fivejjs/GPy,strongh/GPy