Basic test in tokamak geometry working

o boutdata.mms.SimpleTokamak class creates metric tensors
  and writes input files for a simplified tokamak input
  -> No x-points, not in equilibrium, quite weak shaping

o MMS/tokamak test with bracket method and Delp2 operator
  converges correctly. Still need to add 1st order terms to Delp2
  (laplace:all_terms = false at the moment)