Binary VTK output
Found this in deal.II: https://github.com/dealii/dealii/blob/1cf12e90abedcf5272eb4c4d916a059c36c7e0c7/source/base/data_out_base.cc#L1269-L1279
```cpp
if (flags.data_binary)
{
stream.write(reinterpret_cast<const char *>(values.data()),
values.size() * sizeof(data));
}
else
{
for (unsigned int i = 0; i < values.size(); ++i)
stream << '\t' << values[i];
stream << '\n';
}
```
issue