The simplest CMake setup possible

Hi, 

I've added a `CMakeLists.txt` file to provide initial support for cmake. **Arcadia** now builds correctly on the Mac OS X 10.9.x. 

Usage:

1. Create a **build** directory and `cd` into it
2. Type `cmake ../` to generate a `Makefile` in linux and mac os x. 

If this is of interest to you, you can accept the pull request. 

Thank you for creating **Arcadia** :)