Install a CMake config to enable find_package(libhandlegraph)

[adamnovak]

Now if you find_package(libhandlegraph), and the CMAKE_INSTALL_PREFIX that libhandlegraph installed into is in your CMAKE_PREFIX_PATH, you will see libhandlegraph::handlegraph_static and libhandlegraph::handlegraph_shared targets, and $libhandlegraph_FOUND will be true.

If you want to fall back to a bundled libhandlegraph, you can poll that variable and, if it isn't set, add libhandlegraph as a subdirectory and alias is targets into the namespace, and then you can just use the namespaced targets for the rest of the build.

[adamnovak]

The CMake code for this is mostly copied out of the documentation at https://cmake.org/cmake/help/latest/manual/cmake-packages.7.html#creating-packages