message: Fix discrepancies between doc and implementation for math_ops
  In the docstring of math_ops, there are some discrepancies
  between the supported data types and the actual implementation:
  `abs` supports `float16`.
diff: @@ -125,8 +125,8 @@ def abs(x, name=None): # pylint: disable=redefined-builtin
  ```
  Args:
  - x: A `Tensor` or `SparseTensor` of type `float32`, `float64`, `int32`,
  - `int64`, `complex64` or `complex128`.
  + x: A `Tensor` or `SparseTensor` of type `float16`, `float32`, `float64`,
  + `int32`, `int64`, `complex64` or `complex128`.
  name: A name for the operation (optional).
  Returns:
  