* add TF sign op

* fix TF squeeze bug

* fix TF expandDims bug

* support squeeze_dims is empty

* delete TF stridedslice op input type is bool

* support TF infer_tensor func input type is int

* fixed stridedslice bug

* fix the code

* fix the visit_tuple

* Update stargan.md

* Update ultra_light_fast_generic_face_detector.md

* fix the docs

* remove static

* fix

* fix

* fix

* fix the docs
Co-authored-by: Nchanningss <chen_lingchi@163.com>

* fix the convert.py args

* fix teh pad and add log_softmax

* add BatchToSpaceND and SpaceToBatchND op convert

* deal with comments

    When use `python setup.py install`, it will report a error:

    ```
    File "/root/miniconda3/lib/python3.7/site-packages/x2paddle-0.7.2-py3.7.egg/x2paddle/op_mapper/tf_op_mapper.py", line 88
        if self.graph.get_node(name).layer_type != "Placeholder"
                                                                ^
    SyntaxError: invalid syntax
    ```

    This commit will resolve the problem.