Add support for CMake find_package command to msgpack. The package
exports the two targets msgpackc-static and msgpackc if shared is
enabled. The CMake find_package command works after installation
of msgpack and during build of another project which adds msgpack
as sub project via add_subdirectory command.
Signed-off-by: Stefan Herbrechtsmeier <stefan.herbrechtsmeier@weidmueller.com>
