* CMake: Add option to set the package install dir.
* CMake: Fix generated config.
- `YAML_CPP_SHARED_LIBS_BUILT` should not be set with a `PATH_VAR` as it
would always evaluate to true.
- `YAML_CPP_LIBRARIES` should used the exported target name including
the namespace, but `check_required_components` shouldn't.
- Use `CMAKE_CURRENT_LIST_DIR` to find the target file, instead of a
`PATH_VAR`. Package managers such as vcpkg move CMake configs after
installing.
* CI: Test the generated CMake package.
* CMake: Create add a deprecated yaml-cpp target.
This target is meant to provide compatibility with versions prior to
0.8.0.
* CMake: mark the yaml-cpp target as IMPORTED.
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Co-authored-by: Jesse Beder <jbeder+github@gmail.com>
