《Android 基础（四十)》 FlexboxLayout

1. 简介

Flexbox-layout，是Google推出的流式布局。具体的基本介绍可以参考Github上的Wiki。看一下类的英文说明：

/**
* A layout that arranges its children in a way its attributes can be specified like the
* CSS Flexible Box Layout Module.
* This class extends the {@link ViewGroup} like other layout classes such as {@link LinearLayout}
* or {@link RelativeLayout}, the attributes can be specified from a layout XML or from code.
*
* The supported attributes that you can use are:
* <ul>
* <li>{@code flexDirection}</li>
* <li>{@code flexWrap}</li>
* <li>{@code justifyContent}</li>
* <li>{@code alignItems}</li>
* <li