Mlgame

**Added**

* Arkanoid and Pingpong:
* The serving position and direction of the ball can be decided
* Add difficulties for different mechanisms
* Add ball slicing mechanism
* Arkanoid: Add hard bricks
* Pingpong: Add blocker

**Changed**

* Update the python from 3.5 to 3.6: For the `auto()` of the custom `Enum`
* Optimize the output of the error message
* Refactor the game classes: Extract the drawing and recording functions
* Add prefix to the filename of the record files
* Physics: Optimize the ball bouncing algorithm

**Added**

* New game - Snake
* Add README to the game Arkanoid and Pingpong

**Changed**

* Update pygame from 1.9.4 to 1.9.6
* Arkanoid and Pingpong (Follow the structure of the game Snake):
* Move `SceneInfo` to the `gamecore.py`
* Rename `GameInstruction` to `GameCommand`
* Arkanoid: Add `command` member to `SceneInfo`
* Trying to load the record files generated before beta 4.1 will get `AttributeError: 'SceneInfo' object has no attribute 'command'` error.
* Code refactoring

**Added**

* `mlgame` - MLGame development API
* `--input-module` flag for specifying the absolute importing path of user modules

**Changed**

* Use 4 spaces instead of tab
* Support one shot mode in the manual mode
* Fit the existing games to the new API
* Move the directory of game to "games" directory
* Arkanoid: Wait for the ml process before start new round
* Arkanoid: Change the communication API

**Changed**

* Pingpong: Exchange the 1P and 2P side
* Code refactoring

**Changed**

* Pingpong: Set the height of the platform from 10 to 30
* Optimize the collision detection algorithm

**Added**

* 2P game "pingpong"

**Changed**

* Optimize the call stack message of ml process
* Use `argparse` instead of `optparse`