TensorFlow Federated 0.76.0

Release 0.76.0

Major Features and Improvements

• Added a Literal to the TFF language, part 2. This change updates the
  tracing and execution portions of TFF to begin using the Literal.
• Added an implementation of the Adafactor optimizer to
  tff.learning.optimizers.build_adafactor
• Added a new field, content, to the Data proto.

Breaking Changes

• Removed the check_foo() methods on building blocks.
• Removed tff.data, this symbol is not used.

Bug Fixes

• Fix a bug where the pip package default executor stack cannot execute
  computations that have Lambdas under sequence_* intrinsics.