do not constrain version (#59)

Consistent information about VTK XML file formats, in particular on
versions, is not available.
Since recent versions of the VTK library still write out files labelled
as version 0.1, not enforcing a particular version seems to be the best
option at the moment.

Co-authored-by: Hendrik Ranocha <[email protected]>

src/ReadVTK.jl

@@ -28,7 +28,7 @@ Hold all relevant information about a VTK XML file that has been read in.
 - `filename`: original path to the VTK file that has been read in
 - `xml_file`: object that represents the XML file
 - `file_type`: currently only `"UnstructuredGrid"` or `"ImageData"` are supported
-- `version`: VTK XML file format version (v1.0 or later)
+- `version`: VTK XML file format version
 - `byte_order`: can be `LittleEndian` or `BigEndian` and must currently be the same as the system's
 - `compressor`: can be empty (no compression) or `vtkZLibDataCompressor`
 - `appended_data`: in case of appended data (see XML documentation), the data is stored here for
@@ -62,7 +62,7 @@ mutable struct VTKFile
   end
 end
 
-# Header type is hardcoded and corresponds to VTK XML version 1.0
+# Header type is hardcoded
 header_type(::VTKFile) = UInt64
 
 # Return true if data is compressed (= XML attribute `compressor` is non-empty in VTK file)
@@ -124,9 +124,6 @@ function VTKFile(filename)
     error("Unsupported file type: ", file_type)
   end
 
-  # Ensure correct version
-  @assert version >= v"1.0"
-
   # Ensure matching byte order
   is_little_endian = ENDIAN_BOM == 0x04030201
   @assert ((byte_order == "LittleEndian" && is_little_endian) ||
@@ -213,7 +210,7 @@ Hold all relevant information about a Parallel VTK XML file that has been read i
 - `filename`: original path to the PVTK file that has been read in
 - `xml_file`: xml info
 - `file_type`: currently only `"PRectilinearGrid"` or `"PImageData"` are supported
-- `version`: VTK XML file format version (v1.0 or later)
+- `version`: VTK XML file format version
 - `vtk_filenames`: vector with strings that contain the filenames of each of the parallel files
 - `vtk_files`: vector with `VTKFile` data that contains the info about each of the files
 """
@@ -257,9 +254,6 @@ function PVTKFile(filename; dir = "")
     error("Unsupported file type: ", file_type)
   end
 
-  # Ensure correct version
-  @assert version >= v"1.0"
-
   # Extract names of files & load the data
   pieces = root[file_type][1]["Piece"]
   n_pieces = length(pieces)
@@ -322,9 +316,6 @@ function PVDFile(filename)
     error("Unsupported PVD file type: ", file_type)
   end
 
-  # Ensure correct version
-  @assert version >= v"1.0"
-
   # Extract names of files & load the data
   pieces = root[file_type][1]["DataSet"]
   n_pieces = length(pieces)