* refine Assign

* add UT

* Support Py3 type annotations in @to_static

* support type hint for args in func

* support type hint assign

* if annotation and value(Constant) are diffent type, we use value type

* polish type_from_annotation()

* code format

* code format

* remove useless commentary

* fix review
Co-authored-by: NAurelius84 <zhangliujie@baidu.com>

* integrated gast library

* integrated gast library

* fix unittest and remove ast2.py

* remove 'gast' from __all__ in __init__.py

* add copyright in other files

* fix copyright

* BugFix StaticAanlysis with gast.Subscript

* remove codes

Add assert grammar for ProgramTranslator

* fix bug with `if Tensor` in is_control_flow test=develop

* remove continue test=develop

* add print transformer & unify print format, test=develop

* remove using of dygraph_to_static_func, test=develop

* remove python stdout capture, test=develop

* fix compatibility problems for PY2, test=develop

* fix detail error, test=develop

* fix type analysis bug, test=develop

* fix print tuple compatible error in PY2, test=develop

* replace get_func to declarative, test=develop

* fix detail bug, test=develop

* fix some detail problems, test=develop

* change visit_call in print transformer, test=develop

1. Add data_layer_not_check because it is needed in dygraph_to_static where input can be variable size
2. Remove warnings in static analysis because python cannot do exact static analysis

* Support Parameter type determination test=develop

* Support Tensor.shape in control flow if/for/while and separate TensorShapeTransformer from BasicApiTransformer. test=develop

+ Refine code structure and move code related with control flow `if` into `ifelse_transformer.py`
+ Merge code of `ast_utils.py`  into `utils.py` 

* Support fetch and run program in the process of dygraph_to_static_output. test=develop

* fix to_source(gast) and remove dygraph API such as Conv2D, Linear. test=develop

1. Considering functions, I have to change the node type from single value to a set. Because python function is allowed to return different types. The set represent all possible types

2. I added scope_name and scope_type for AstVarScope, because in python functions, variable may have different scope. For example:

```
a = 3
def foo(b):
    a = 9
    return a + b
```

the `a` in `foo` is different to the `a` out of `foo`. Similar to class field. The scope_name will help me to know the function name when static analysis finds a `return` sentence.

* add is_control_flow_if  test=develop

1. Move AstNodeWrapper, StaticAnalysisVisitor to a new python file: static_analysis.py
2. Add basic node var type analysis