CMake rewrite

[SamuelMarks]

WiP. If you want me to finish this just @ me.

[hmgle]

Well done. Looking forward to your finishing.

[SamuelMarks]

Ok it's pretty much done. Just need to test on Linux.

Will probably need a couple of additional find_package and target_link_libraries.

Have you considered rewriting with libevent or libuv?

[hmgle]

Ok it's pretty much done. Just need to test on Linux.

Will probably need a couple of additional find_package and target_link_libraries.

Have you considered rewriting with libevent or libuv?

@SamuelMarks Sorry, I missed the progress of this work. For the other libraries libevent and libuv, I think if rewriting can make the code simpler or more maintainable, then it's worth doing. I have no experience in using libuv, but it looks great.