Add button images.

http://www.raywenderlich.com/18840/how-to-make-a-simple-drawing-app-with-uikit
http://cdn2.raywenderlich.com/downloads/DrawPadGraphics.zip
Merge branch 'master' of https://github.com/touchvg/iOSHelloWorld into ColorPad
Update README.md
可以修改笔刷透明度和颜色
可以设置笔刷宽度
添加了对直线图元的使用

点击shape按钮选择line
写作业去了。。。
明天把helper改成局部变量
然后再试试其他command
按照上次PR时受到的回复进行了修改

1 change helper to local Local variables.
2 use erase reset save.
3 use ios7 AutoLayout to fit the screen. And change the color of UIView
(i think i’ll change it back to white after deal the GiPaintView resize
problem.)
4 try to add redo & undo but failed.
5 delete useless code.
6 change some @property to static method
7 add more cmd to shapeAction sheet
更改了几个图标，更改工程从universe到iPhone，
加入redo&undo。又改了几个图标。