Merge branch 'feature/automatically-add-pthread' into 'master'

ref:extensions/dune-codegen this need cmake 3.1, if the cmake version should
stay at 2.8 I could find another way to link it.

fixes [#153]

See merge request [extensions/dune-codegen!337]

  [#153]: gitlab.dune-project.org/NoneNone/issues/153
  [extensions/dune-codegen!337]: gitlab.dune-project.org/extensions/dune-codegen/merge_requests/337


Closes #153