Merge branch 'add_polyhedron_support' into 'master'
Add support for Polyhedron cells Elements of type Polyhedron (i.e. N face cells, where each face is a M edge polygon) are in the following format: [nCellFaces, nFace0Pts, id0_0, id0_1, ..., nFace1Pts, id1_0, id1_1, ..., ...] This has first been proposed in a MR to VTK (vtk/vtk!1255), which contains the necessary changes to VTK. The VTK MR also has example/test files attached that demonstrated the functionality. Ping: @demarle See merge request !5