logical plan & physical plan;
explain;
yacc rewrite;
join operator(nested loop join);
simple rewrite rules;
fix some issues of mysql protocol;

tested by mariadb ( Ver 15.1 Distrib 5.5.65-MariaDB, for Linux (x86_64) using readline 5.1)
but failed with obclient

2022 oceanbase competition

* 简化git submodule操作

* support build with address sanitizer

using cmake options `-DENALBE_ASAN=ON` to enable address sanitizer

* fix some memory leaks detected by asan

* stage线程分配问题 #75
* 客户端连接可以指定host和port

优化load data效率

* stage线程分配问题 #75

* 设置线程名称，在top时显示线程名，便于调试

没有为stage分配配置的线程池，而使用了默认线程池

add copyright header info

Other improvement
1. add code format file
2. add gitignore
3. add memory pool utility
4. remove useless file mpool.h, index_manager.cpp/h
5. rename the interface of disk_buffer_pool basing on the new mem_pool
6. add some logs in db/table/disk_buffer_pool
7. add unit test mem_pool_test/log_test/bplus_tree_test
8. code format all modified files
9. redefine the interface of table_meta
10. change log's  full path as file name
11. add utility function, print_callstack, remove warning of path