First stab at hayai-config.cmake setup

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

TODO: move public headers to include/hayai or tweak /src in CONF_INCLUDE_DIRS
Merge pull request #4 from mloskot/hayai-config.cmake

First stab at hayai-config.cmake setup