resolved issues in zarr-python

[MSanKeys963]

Linking this from #54. The following issues have been completed, accompanied by a PR. We can safely close them as completed. Here are my suggestions for resolved issues in zarr-python:

• Fixing minor errors in documentation zarr-python#1234 - Issue closed
  • PR: Fix minor indexing errors in tutorial and specification examples of d… zarr-python#1277 - PR merged
• Inconsistent listdir() and rmdir() method signature across class hierarchy zarr-python#890
  • PR: Consistent signatures for listdir() and rmdir() zarr-python#903

If you think this is in the right category, feel free to merge the PR and close the issue. Thanks!