Atlas-2.1

New features:

1. Support multiple MySQL clients: MySQL Workbench, Navicat and SQLyog.
2. The master can be a slave for reading.
3. Forbid the update sqls that have no 'where' condition.
4. Add the informations about server port and client port in sql log.
5. Remove the config options: admin-lua-script and instance.
6. Each thread has a connection pool to backend.

Bug fix:

1. Fix bug of the config option:charset doesn't work
2. Fix bug of update/delete operate in sharding.