Add contrib/mariadbclient

[hfcrwx]

MariaDB Async Client
Using Non-blocking API

Reference:
https://mariadb.com/kb/en/using-the-non-blocking-library/
https://github.com/MariaDB/server/blob/5.5/client/async_example.c
https://github.com/MariaDB/server/blob/5.5/tests/async_queries.c
https://mariadb.com/kb/en/non-blocking-api-reference/

Build:
centos7-x86_64:
yum install mariadb-devel mariadb-libs
ubuntu14.04-x86_64:
apt-get install libmariadbclient-dev
ln -sf libmariadbclient.so libmysqlclient.so

[chenshuo]

Please fix travis-ci first, put apt-get install in .travis.yml.

[chenshuo]

I haven't read the contrib/mariadhclient/ part, will do it later.

[chenshuo]

I suggest not to introduce the new classify parameter. Instead, if EventsCallback is provided, it intercepts all events.

[hfcrwx]

Do you mean change
channel_->setEventsCallback(std::bind(&MariaDBClient::stateMachineHandler, this, kRealConnectCont, _1, 2));
to
channel->setReadCallback(std::bind(&MariaDBClient::stateMachineHandler, this, kRealConnectCont, _1, 2));
channel->setWriteCallback(std::bind(&MariaDBClient::stateMachineHandler, this, kRealConnectCont, _1, _2));
?

[chenshuo]

Parameter events__ -> events.

[hfcrwx]

on centos7-x86_64:
if events__ -> events
错误：‘events’的声明隐藏了‘this’的一个成员 [-Werror=shadow]
events shadows int events()

ref:
Channel::Channel(EventLoop* loop, int fd__, bool classify)

[hfcrwx]

Update:

1. zero copy MYSQL_RES:
   mysql_use_result, mysql_fetch_row_* -> mysql_store_result_*
   use new callback function: std::function<void(MariaDBClient*, MYSQL_RES*)>

2. change MariaDBClient to a single-threaded version (as Hiredis, Curl)

3. refactors

Test successfully with MariaDB-Server/MySQL-Server

ref:
https://mariadb.com/kb/en/non-blocking-api-reference/
https://dev.mysql.com/doc/refman/5.7/en/mysql-store-result.html