Add exit statuses to all validate scripts
Comments and error checking in midpoint method
Remove the almost useless "MyDocInfo" class
Major improvements to MyCliArgs

* Add factory functions for runtime specification of:
** mesh
** timesteppers
** applied field
** initial magnetisation

* Add generic set of initial magnetisations and applied fields

* Modify element + problem to use functions passing vectors by value
  Using return value optimisation.
Make the midpoint method self test *only* be a self test
Fiddling with nmag rectangle example
Include proper timestepper weights in micromagnetics Jacobian
Small updates to fix compatability with new code
Small fixes to get simple rigorous exchange test working again