Fix issue 412 where an HDF dataset or group was not closed.
  -- Add support for using HDF5File and other Files in a with statement.
  -- Add HDF5Attribut.list_attributes() which returns a list of str of attributes
Add python container interface for HDFAttributes letting you do stuff like:

  if "key" in attr:
      ...
  for "key" in attr:
      ...
  for value in attr.values():
      ...
  for key, value in attr.items():
      ...

Add unit test for all new features.
Add missing tests
Fix a typo