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

Issue Number: close #191 

Problem:
doxy文档的首页没有描述

### What is changed and how it works?
增加首页描述信息，写在了main.cpp中

### Other information

### 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