From: @limingqi107
Reviewed-by: @cristoval,@wilfchen
Signed-off-by: @wilfchen

From: @ding_fei_fei
Reviewed-by: 
Signed-off-by:

The basic idea is: exploits data dependency to control the execution order
of side-effect operations, and keep the semantics of ANF unchanged.

The ControlDepend primitive is removed and there are two primitives added:

1. UpdateState:
```
  a = Assign(para, value)
```
became:
```
  a = Assign(para, value, u)
  u = UpdateState(u, a)
```

2. Load:
```
  x = Add(para, value)
```
became:
```
  p = Load(para, u)
  x = Add(p, value)
  u = UpdateState(u, p)
```

From: @jojobugfree
Reviewed-by: 
Signed-off-by:

Merge pull request !8036 from chenweifeng/BnAddReluGrad-check

Merge pull request !7767 from VectorSL/readme

Merge pull request !6971 from chenweifeng/tensoradd_inplace

Merge pull request !6825 from VectorSL/combine-cast

Merge pull request !5612 from chenweifeng/BatchNormAddReluGrad