Implementation of `sizeof`

[amontoison]

It could be relevant to know the storage used by a stats or a solver sometimes.
I implemented my own function in Krylov.jl but it can be used here too for optimization solvers.

function ksizeof(attribute)
  if isa(attribute, AbstractVector) && !isempty(attribute)
    # All vectors inside a vector have the same size in Krylov.jl
    size_attribute = length(attribute) * ksizeof(attribute[1])
  else
    size_attribute = sizeof(attribute)
  end
  return size_attribute
end

function sizeof(stats_solver :: Union{KrylovStats, KrylovSolver})
  type = typeof(stats_solver)
  nfields = fieldcount(type)
  storage = 0
  for i = 1:nfields
    field_i = getfield(stats_solver, i)
    size_i = ksizeof(field_i)
    storage += size_i
  end
  return storage
end