cmake build

[dvv]

i drafted a cmake build here https://github.com/dvv/luv-1/tree/cmake . please, feedback if it's feasible to have in master.
libzmq just started cmake for windows, libuv has cmake build thanks to @okuoku , luv per se is trivial to cmake-build.

[dvv]

@okuoku: please update your file -- https://github.com/dvv/luv-1/blob/cmake/cmake/uv/CMakeLists.txt. the main difference is libuv has dropped dep on eio. tia

[dvv]

have updated the branch heavily

[dvv]

sent a pr #20