### What problem were solved in this pull request?

Issue Number: close #142 

Problem:
value和tuple_cell的语义是重合的，所以代码时冗余的

### What is changed and how it works?
删除tuple_cell，都使用value来替换，并将tuple_cell中的接口都在value中实现

### Other information

### What problem were solved in this pull request?

Issue Number: ref #165 
ref #174 

Problem:
一些文档需要优化

### What problem were solved in this pull request?

Issue Number: close #173 close #136 

ref #174 
ref #165 

Problem:
这个PR修改了多个问题，可以参考各个issue。包括observer编译两次、代码目录规划不合理、command executor未全部实现等

### What is changed and how it works?
做一些重构优化，包括CMakelist、一些代码目录、command executor