Release v1.4.0

• Added: audformat.Scheme.set_labels()
  to add labels to an existing scheme
  that has none.
  To replace labels
  use audformat.Scheme.replace_labels()
• Added: store audformat version in table files.
  For parquet files it is stored under the audformat-version metadata key.
  Pickle files store now a dictionary with the keys
  audformat-version and df,
  whereas df contains the table data
• Fixed: audformat.utils.hash() for large dataframes.
  Before it resulted in the same hash
  for large dataframes
  that differed only in rows in their center.
  This is a breaking change
  and will result in different hash values.
  When using audb.publish()
  to update a database
  not published with audformat>=1.4.0,
  it will result in republishing all existing tables,
  which is the desired behavior
• Fixed: loading scheme labels from misc table,
  when using audformat.Database.load(..., load_data=True)