added offset to the abfun.
made abfun auto_expandable
fixed documentation for abfun
adjusted FindOnePersonTeGFR to compute long term slope by trt indicator for each time point
fixed bug introduced in the previous change to using trt in FindOnePersonTeGFR.
fix for AcuteModelLinearAttenuationClass so that effect will produce a vector instead of a single value.
fix for AcuteModelLogEffectClass in TrueEGFR.
No effect below egfr <= 15
fix for AdditiveMortalityClass
Fix for computing residual.z
Bug fix for TimeModel
Merge branch 'master' of github.com:jennyteng/CKDsim

Conflicts:
	R/class-AcuteModel.R
	R/class-SlopeModel.R