update documentation: new download page with the downloads counter
new get_t4_from_t2s() helper function
clean up tests/test_tensors.py
update tests/test_tensors.py to test get_t4_from_t2s()
merge pull request #247 from 'vlukes/download_page'
update download page: add recommendation to download the latest release
fix transform_asm_vectors()
fix passing region kind argument in Region.from_facets()
update docstring of Region.__init__()
add parent argument to Region.from_facets()
re-add '2_2', '3_2' to vtk_cell_types
prevent false memory errors after warp violation in dq_finite_strain()
fix docstring of examples/navier_stokes/stokes_slip_bc.py