This creates and installs a package version file and a package config
file. These are used by find_package with the CONFIG option, and are
roughly equivalent to pkgconfig, but is cmake specific rather than linux
specific.

v2: - Use configure_package_config_file() instead of config_file(),
      which generates helper macros and resolves relative paths allowing
      the entire install to be moved.
    - Update WaffleConfig.cmake.in to take advantage of
      configure_package_config_file()
    - Use SameMajorVersion instead of AnyNewerVersion for version
      compatibility. Since waffle uses apache's numbering scheme 2.0.0
      should not fulfill a requirement of 1.5.0 and vice versa.
v3: - Use CMAKE_BINARY_DIR (Jordan)
    - Move generation of cmake config to the same area of the cmake file
      as pkgconfig

Signed-off-by: Dylan Baker <dylanx.c.baker@intel.com>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>