Supporting CMake build

Hi dear maintainer,

First I would like to express my gratitude for your open sourcing this library. As an ex-googler I am getting pretty used to recordio and this is exactly what I need in my use cases.

In one of my recent project I need to add this library as a cmake dependency. Tried to search in the issues but seems no one is mentioning having CMake support. I personally think CMake is still popular among the open source world and it might be good if the library support it so that more projects can enjoy the benefit of this library.

Thanks!