Update demag.go to work with new demag tensor.

Added Newell's demagnetizing tensor calculation.
Create newellDemagKernel.go

Added stuff to enable calculation of demagnetizing tensor using Newell's formulation.
Create divide.cu

Needed for relative error calculation in time stepper
Create divide.go

Needed for relative error calculation in time stepper
Create vecnorm.cu

Needed for relative error calculation in time stepper
Create vecnorm.go

Needed for relative error calculation in time stepper
Update heun.go

Updated to include relative error calculation for time stepping
Update rk23.go

Updated to include relative error calculations in time stepping
Update rk45dp.go

Updated to include relative error calculations in time stepping
Update run.go

Updated to support relative error calculations in time stepping
Update demag.go

Point demag.go to Newell's demagnetizing tensor calculation
Merge branch 'kelvin_demag' of https://github.com/xfong/3 into kelvin_merged

Conflicts:
	engine/demag.go
Merge branch 'kelvin_stepper_updates' of https://github.com/xfong/3 into kelvin_merged

Merging edits for kelvin_demag and kelvin_stepper_updates with the the arne branch