Concrete Example of writing ZArr array in C++

[imikejackson]

I've noticed that the examples and tests use either python or GDAL to write a test zarr file. I was looking for an example that uses only the local file system store (NOT GDAL, GZIP, BLOSC or any other compressor) to write data to the zarray and then have that flushed to disk? We have put in a PR for some changes to make GDAL optional at #62 to support this example use case.