Add CMake option for install into moodycamel

Hi,
I tend to use your excellent queues in various placements.

I recently noticed that the concurrentqueue cmake build installs with the ".../moodycamel/" sub-directory.
However, this readerwriterqueue build does not have the moodycamel part.

I tend to root the include directories to work as:
#include <moodycamel/concurrentqueue.h>

As you wouldn't want to break existing code, any chance of a cmake option that would add the "moodycamel/" part into the readerwriterqueue install location?

首先比较 readerwriterqueue 和 concurrentqueue 的 CMake 安装配置，找出 include 目标的定义位置。添加一个用于设置 moodycamel/ 安装前缀的选项，同时保留当前默认值，然后验证已安装的头文件支持所请求的两种布局。