First stab at hayai-config.cmake setup

This is attempt to provide CMake ```find_package``` config mode for hayai project
The configuration is based on the official tutorials:
http://www.cmake.org/Wiki/CMake/Tutorials/How_to_create_a_ProjectConfig.cmake_file
http://www.cmake.org/Wiki/CMake/Tutorials/Exporting_and_Importing_Targets

There is one little details that may need to be improved:
either move public headers to ```${PROJECT_SOURCE_DIR}include/hayai``` or tweak ```${PROJECT_SOURCE_DIR}/src``` in ```CONF_INCLUDE_DIRS``` variable, so the include paths are set properly while importing targets directly from the build directory (a nice CMake feature, by the way).

Generally, I think it would be good to install and use buried headers in hayai sources as well as in client programs, like this:
```
#include <hayai/hayai.hpp>
```